feat(Http): can optionally fetch local resources from app bundle with Http

[NathanWalker]

This provides a nice convenience for Angular developers; an easy way to fetch local files with Http from their app bundle just like they would local files in their web app using the same semantics as NativeScript XML Image src property.

this.http.get(`~/assets/data.json`)
      .map((response: Response) => response.json())
      .subscribe((results: string[]) => {
        // we have results!
      });

... is now possible 👍

[NathanWalker]

This now has tests with helpful mocks 👍

[NathanWalker]

As far as any debate around "is it right to allow Http module to request local files"… the main question is does Http allow local files to be requested from a web server, and the answer is ​_Yes_​. That’s how web devs see it… If a file is in their web app and it can be requested via XMLHttpRequest, which it can, the same expectation will be brought to their approach to {N}… they will want to be able to intutively request files from their app with Http. This was one of those things when I started with nativescript-angular, I just expected to work and didn’t understand why it didnt… since i am a hardened web dev.

Outside of those logical reasons… it is just convenient sugar… and devs love sugar… it’s what makes for a happier dev experience imo.

[NathanWalker]

This PR also fixes the new error occuring for some folks with latest that's in rc2 and rc3 with Http

ORIGINAL EXCEPTION: Error: not implemented
ORIGINAL STACKTRACE:
Error: not implemented
    at NativeScriptDomAdapter.Parse5DomAdapter.getCookie (/data/data/org.nativescript.nativescriptweather/files/app/tns_modules/@angular/platform-server/src/parse5_adapter.js:612:68)

[vakrilov]

👍

[hdeshev]

👍