refactor: export core APIs from angular2/core

This change moves many APIs to the angular2/core export.

This change also automatically adds FORM_BINDINGS in
the application root injector.

BREAKING CHANGE:
    Many dependencies that were previously exported from specific
    APIs are now exported from angular2/core. Affected exports, which
    should now be included from angular2/core include:

    angular2/forms
    angular2/di
    angular2/directives
    angular2/change_detection
    angular2/bootstrap (except for dart users)
    angular2/render
    angular2/metadata
    angular2/debug
    angular2/pipes
Closes #3977

modules/angular2/test/http/backends/jsonp_backend_spec.ts

@@ -14,7 +14,7 @@ import {
 import {ObservableWrapper} from 'angular2/src/core/facade/async';
 import {BrowserJsonp} from 'angular2/src/http/backends/browser_jsonp';
 import {JSONPConnection, JSONPBackend} from 'angular2/src/http/backends/jsonp_backend';
-import {bind, Injector} from 'angular2/di';
+import {bind, Injector} from 'angular2/core';
 import {isPresent, StringWrapper} from 'angular2/src/core/facade/lang';
 import {TimerWrapper} from 'angular2/src/core/facade/async';
 import {Request} from 'angular2/src/http/static_request';

modules/angular2/test/http/backends/xhr_backend_spec.ts

@@ -14,7 +14,7 @@ import {
 import {ObservableWrapper} from 'angular2/src/core/facade/async';
 import {BrowserXhr} from 'angular2/src/http/backends/browser_xhr';
 import {XHRConnection, XHRBackend} from 'angular2/src/http/backends/xhr_backend';
-import {bind, Injector} from 'angular2/di';
+import {bind, Injector} from 'angular2/core';
 import {Request} from 'angular2/src/http/static_request';
 import {Response} from 'angular2/src/http/static_response';
 import {Headers} from 'angular2/src/http/headers';

modules/angular2/test/http/http_spec.ts

@@ -11,7 +11,7 @@ import {
   xit,
   SpyObject
 } from 'angular2/test_lib';
-import {Injector, bind} from 'angular2/di';
+import {Injector, bind} from 'angular2/core';
 import {MockBackend, MockConnection} from 'angular2/src/http/backends/mock_backend';
 import {EventEmitter, ObservableWrapper} from 'angular2/src/core/facade/async';
 import {