fix: unable to create project from scoped package template

[rosen-vladimirov]

In case you try to create application from scoped package, for example @nativescript/some-package-name, CLI fails with npm install error.
The problem is that CLI thinks everything after @ is a version and sets the package name that has to be installed to empty string.
Fix the parsing and add tests

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behavior?

The following command fails:

tns create myApp --template "@angular/core" 

What is the new behavior?

The following command succeeds:

tns create myApp --template "@angular/core" 

Fixes issue #3934