feat(core): add support for @Property and @Event decorators

Example:

@Directive({selector: 'my-selector'})
class MyDirective {
  @Property() prop;
  @Property('el-prop') prop2;
  @Event() event;
  @Event('el-event') event2;
}

Closes #3992

modules/angular2/metadata.ts

@@ -34,7 +34,13 @@ export {
   QueryFactory,
   ViewQuery,
   Pipe,
-  PipeFactory
+  PipeFactory,
+  Property,
+  PropertyFactory,
+  PropertyMetadata,
+  Event,
+  EventFactory,
+  EventMetadata
 } from './src/core/metadata';
 
 export {