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/src/core/testability/testability.ts

@@ -1,4 +1,4 @@
-import {Injectable} from 'angular2/di';
+import {Injectable} from 'angular2/src/core/di';
 import {DOM} from 'angular2/src/core/dom/dom_adapter';
 import {Map, MapWrapper, ListWrapper} from 'angular2/src/core/facade/collection';
 import {StringWrapper, isBlank, BaseException} from 'angular2/src/core/facade/lang';