refactor(compiler): rename decorator directives into directive

BREAKING CHANGE:
Previously, `Directive` was the abstract base class of several directives.
Now, `Directive` is the former `Decorator`, and `Component` inherits from it.

modules/angular2/src/core/annotations/annotations.es6

@@ -5,7 +5,6 @@
 
 export {
   Component as ComponentAnnotation,
-  Decorator as DecoratorAnnotation,
   Directive as DirectiveAnnotation,
   onDestroy, onChange, onAllChangesDone
 } from '../annotations_impl/annotations';