refactor(core): separate reflective injector from Injector interface

BREAKING CHANGE:
- Injector was renamed into `ReflectiveInjector`,
  as `Injector` is only an abstract class with one method on it
- `Injector.getOptional()` was changed into `Injector.get(token, notFoundValue)`
  to make implementing injectors simpler
- `ViewContainerRef.createComponent` now takes an `Injector`
  instead of `ResolvedProviders`. If a reflective injector
  should be used, create one before calling this method.
  (e.g. via `ReflectiveInjector.resolveAndCreate(…)`.

modules/angular2/test/platform/browser/tools/spies.dart

@@ -1,5 +1,5 @@
 import 'package:angular2/testing_internal.dart' show SpyObject;
-import 'package:angular2/core.dart' show Injector, bind;
+import 'package:angular2/core.dart' show Injector, ReflectiveInjector, bind;
 import 'package:angular2/src/core/application_ref.dart' show ApplicationRef;
 import 'package:angular2/src/core/linker/component_factory.dart'
     show ComponentRef;
@@ -15,7 +15,7 @@ class SpyComponentRef extends SpyObject implements ComponentRef {
   Injector injector;
 
   SpyComponentRef() {
-    this.injector = Injector
+    this.injector = ReflectiveInjector
         .resolveAndCreate([bind(ApplicationRef).toClass(SpyApplicationRef)]);
   }
 }

modules/angular2/test/platform/browser/tools/spies.ts

@@ -1,5 +1,5 @@
 import {SpyObject} from 'angular2/testing_internal';
-import {Injector, provide} from 'angular2/core';
+import {ReflectiveInjector, provide} from 'angular2/core';
 import {global} from 'angular2/src/facade/lang';
 import {ApplicationRef, ApplicationRef_} from 'angular2/src/core/application_ref';
 
@@ -11,8 +11,8 @@ export class SpyComponentRef extends SpyObject {
   injector;
   constructor() {
     super();
-    this.injector =
-        Injector.resolveAndCreate([provide(ApplicationRef, {useClass: SpyApplicationRef})]);
+    this.injector = ReflectiveInjector.resolveAndCreate(
+        [provide(ApplicationRef, {useClass: SpyApplicationRef})]);
   }
 }