feat(common): new HttpClient API

HttpClient is an evolution of the existing Angular HTTP API, which exists
alongside of it in a separate package, @angular/common/http. This structure
ensures that existing codebases can slowly migrate to the new API.

The new API improves significantly on the ergonomics and features of the legacy
API. A partial list of new features includes:

* Typed, synchronous response body access, including support for JSON body types
* JSON is an assumed default and no longer needs to be explicitly parsed
* Interceptors allow middleware logic to be inserted into the pipeline
* Immutable request/response objects
* Progress events for both request upload and response download
* Post-request verification & flush based testing framework

package.json

@@ -92,7 +92,7 @@
     "source-map": "^0.5.6",
     "source-map-support": "^0.4.2",
     "systemjs": "0.18.10",
-    "ts-api-guardian": "^0.2.1",
+    "ts-api-guardian": "^0.2.2",
     "tsickle": "^0.21.1",
     "tslint": "^4.1.1",
     "tslint-eslint-rules": "^3.1.0",