feat(ElementInjector): implement ElementInjector

Initial implementation of ElementInjector.

Works:
1. The creation of proto element injector trees
2. Bindings
3. The instantiation of element injectors
4. The instantiation of directives
5. Visibility: Parent and Ancestor
6. Delegation to application injectors
7. Error handling

Missing features:
1. Handling components.
2. Setting "special" properties (e.g., Element, View).
3. Cycle detection
4. Distance
5. Text nodes
That's true. My benchmarks, however, showed no performance increase.  Also, once https://github.com/angular/angular/pull/101 makes it into master, I will change `ElementInjector` to call `_getDirectiveByKey` only when resolving directives.