refactor(core): move facades out of core

This is part of ongoing work to make core platform-independent.

BREAKING CHANGE

All private exports from 'angular2/src/core/facade/{lang,collection,exception_handler}' should be replaced with 'angular2/src/facade/{lang,collection,exception_handler}'.

modules/angular2/test/core/reflection/reflector_spec.ts

@@ -18,7 +18,7 @@ import {
   propDecorator,
   HasGetterAndSetterDecorators
 } from './reflector_common';
-import {IS_DART} from 'angular2/src/core/facade/lang';
+import {IS_DART} from 'angular2/src/facade/lang';
 
 class AType {
   value;