feat(core): introduce template context

BREAKING CHANGE:
- Before, a `EmbeddedViewRef` used to have methods for 
  setting variables. Now, a user has to pass in a context
  object that represents all variables when an `EmbeddedViewRef`
  should be created.
- `ViewContainerRef.createEmbeddedViewRef` now takes
   a context object as 2nd argument.
- `EmbeddedViewRef.setLocal` and `getLocal` have been removed.
  Use `EmbeddedViewRef.context` to access the context.
- `DebugNode.locals` has been removed. Use the new methods `DebugElement.references`
  to get the references that are present on this element,
  or `DebugElement.context` to get the context of the `EmbeddedViewRef` or the component to which the element belongs.

Closes #8321

modules/angular2/test/core/debug/debug_node_spec.ts

@@ -338,7 +338,7 @@ export function main() {
              .then((fixture) => {
                fixture.detectChanges();
 
-               expect(fixture.debugElement.children[0].getLocal('alice')).toBeAnInstanceOf(MyDir);
+               expect(fixture.debugElement.children[0].references['alice']).toBeAnInstanceOf(MyDir);
 
                async.done();
              });