Improve Windows setup script

Changes include:
    * Asking permission from user for every installation - this includes an `all` option for eliminating subsequent questions
    * Improved error handling - warning upon non-zero exit code
    * Initial check for latest .NET Framework installed - should be at least 4
    * Check for correct Chocolatey installation
    * Fixed the syntax in docs header on invoking the setup script from the command prompt
    * Added example syntax in docs header for invoking the setup script from powershell itself

Author: Dimitar Kerezov

setup/native-script.ps1

@@ -1,30 +1,76 @@
 
 # A PowerShell script to set up Windows machine for NativeScript development
-# To run it against the PRODUCTION branch (only one supported with self-elevation) use
-# @powershell -NoProfile -ExecutionPolicy Bypass -Command "iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/NativeScript/nativescript-cli/production/setup/native-script.ps1'))" 
+# NOTE: The scripts requires at least a version 4.0 .NET framework installed
+# To run it inside a COMMAND PROMPT against the production branch (only one supported with self-elevation) use
+# @powershell -NoProfile -ExecutionPolicy Bypass -Command "iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/NativeScript/nativescript-cli/production/setup/native-script.ps1'))"
+# To run it inside a WINDOWS POWERSHELL console against the production branch (only one supported with self-elevation) use
+# iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/NativeScript/nativescript-cli/production/setup/native-script.ps1'))
+
+# Check if latest .NET framework installed is at least 4
+$dotNetVersions = Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP' -recurse | Get-ItemProperty -name Version,Release -EA 0 | Where { $_.PSChildName -match '^(?!S)\p{L}'} | Select Version
+$latestDotNetVersion = $dotNetVersions.GetEnumerator() | Sort-Object Version | Select-Object -Last 1
+$latestDotNetMajorNumber = $latestDotNetVersion.Version.Split(".")[0]
+if ($latestDotNetMajorNumber -lt 4) {
+	Write-Host -ForegroundColor Red "Running this script requires at least a version 4.0 .NET framework installed"
+	if ((Read-Host "Do you want to open Microsoft's Download Center in your default browser(y/n)") -eq 'y') {
+		Start-Process -FilePath "https://www.microsoft.com/en-us/download/search.aspx?q=.net%20framework&p=0&r=10&t=&s=Relevancy~Descending"
+	}
+
+	exit 1
+}
 
 # Self-elevate
 $isElevated = ([Security.Principal.WindowsPrincipal] [Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole]"Administrator")
 if (-not $isElevated) {
-    start-process -FilePath PowerShell.exe -NoProfile -ExecutionPolicy Bypass -Verb Runas -Wait -Command "iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/NativeScript/nativescript-cli/production/setup/native-script.ps1'))"
-    exit 0
+	start-process -FilePath PowerShell.exe -Verb Runas -Wait -ArgumentList "-NoProfile -ExecutionPolicy Bypass -Command iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/NativeScript/nativescript-cli/production/setup/native-script.ps1'))"
+	exit 0
+}
+
+# Help with installing other dependencies
+$script:answer = ""
+function Install($programName, $message, $script, $shouldExit) {
+	if ($script:answer -ne "a") {
+		Write-Host -ForegroundColor Green "Allow the script to install $($programName)?"
+		Write-Host "Tip: Note that if you type a you won't be prompted for subsequent installations"
+		do {
+			$script:answer = (Read-Host "(Y)es/(N)o/(A)ll").ToLower()
+		} until ($script:answer -eq "y" -or $script:answer -eq "n" -or $script:answer -eq "a")
+
+		if ($script:answer -eq "n") {
+			Write-Host -ForegroundColor Yellow "You have chosen not to install $($programName). Some features of NativeScript may not work correctly if you haven't already installed it"
+			return
+		}
+	}
+
+	Write-Host $message
+	Invoke-Expression($script)
+	if ($LASTEXITCODE -ne 0) {
+		Write-Host -ForegroundColor Yellow "WARNING: $($programName) not installed"
+	}
 }
 
+function Pause {
+	Write-Host "Press any key to continue..."
+	[void][System.Console]::ReadKey($true)
+}
+
+# Actually installing all other dependencies
 # Install Chocolately
-iex ((new-object net.webclient).DownloadString('https://chocolatey.org/install.ps1'))
+Install "Chocolately(It's mandatory for the rest of the script)" "Installing Chocolately" "iex ((new-object net.webclient).DownloadString('https://chocolatey.org/install.ps1'))"
 
-# install dependenciess with Chocolately
+if ((Get-Command "cinst" -ErrorAction SilentlyContinue) -eq $null) {
+	Write-Host -ForegroundColor Red "Chocolatey is not installed or not configured properly. Download it from https://chocolatey.org/, install, set it up and run this script again."
+	Pause
+	exit 1
+}
 
-write-host "To ensure consistent environment, this script will re-install all NativeScript dependencies."
+# Install dependenciess with Chocolately
 
-write-host -BackgroundColor Black -ForegroundColor Yellow "Installing Google Chrome (required to debug NativeScript apps)"
-cinst googlechrome --force --yes
+Install "Google Chrome" "Installing Google Chrome (required to debug NativeScript apps)" "cinst googlechrome --force --yes"
 
-write-host -BackgroundColor Black -ForegroundColor Yellow "Installing Java Development Kit"
-cinst jdk8 --force --yes
+Install "Java Development Kit" "Installing Java Development Kit" "cinst jdk8 --force --yes"
 
-write-host -BackgroundColor Black -ForegroundColor Yellow "Installing Android SDK"
-cinst android-sdk --force --yes
+Install "Android SDK" "Installing Android SDK" "cinst android-sdk --force --yes"
 
 # setup android sdk
 echo yes | cmd /c "$env:localappdata\Android\android-sdk\tools\android" update sdk --filter "tools,platform-tools,android-23" --all --no-ui
@@ -33,17 +79,16 @@ echo yes | cmd /c "$env:localappdata\Android\android-sdk\tools\android" update s
 # setup environment
 
 if (!$env:ANDROID_HOME) {
-    [Environment]::SetEnvironmentVariable("ANDROID_HOME", "$env:localappdata\Android\android-sdk", "User")
-    $env:ANDROID_HOME = "$env:localappdata\Android\android-sdk";
+	[Environment]::SetEnvironmentVariable("ANDROID_HOME", "$env:localappdata\Android\android-sdk", "User")
+	$env:ANDROID_HOME = "$env:localappdata\Android\android-sdk";
 }
 
 if (!$env:JAVA_HOME) {
 	$curVer = (Get-ItemProperty "HKLM:\SOFTWARE\JavaSoft\Java Development Kit").CurrentVersion
 	$javaHome = (Get-ItemProperty "HKLM:\Software\JavaSoft\Java Development Kit\$curVer").JavaHome
 	[Environment]::SetEnvironmentVariable("JAVA_HOME", $javaHome, "User")
-    $env:JAVA_HOME = $javaHome;
+	$env:JAVA_HOME = $javaHome;
 }
 
-write-host -BackgroundColor Black -ForegroundColor Yellow "This script has modified your environment. You need to log off and log back on for the changes to take effect."
-Write-Host "Press any key to continue..."
-[void][System.Console]::ReadKey($true)
+Write-Host -ForegroundColor Green "This script has modified your environment. You need to log off and log back on for the changes to take effect."
+Pause