refactor: rename annotations to metadata

BREAKING CHANGE (maybe)

Well as long as our customers use public API this should not be a
breaking change, but we have changed import structure as well as
internal names, so it could be breaking.

import:
  angular2/annotations => angular2/metadata

Classes:
  *Annotations => *Metadata
  renderer.DirectiveMetadata => renderer.RendererDirectiveMetadata
  renderer.ElementBinder => renderer.RendererElementBinder
  impl.Directive => impl.DirectiveMetadata
  impl.Component => impl.ComponentMetadata
  impl.View => impl.ViewMetadata

Closes #3660

modules/angular2/src/core/application_common.ts

@@ -359,12 +359,12 @@ export class ApplicationRef {
   }
 
   /**
-   * Returns the current {@link Component} type.
+   * Returns the current {@link ComponentMetadata} type.
    */
   get hostComponentType(): Type { return this._hostComponentType; }
 
   /**
-   * Returns the current {@link Component} instance.
+   * Returns the current {@link ComponentMetadata} instance.
    */
   get hostComponent(): any { return this._hostComponent.instance; }