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/transform/directive_processor/transformer.dart

@@ -16,7 +16,7 @@ import 'rewriter.dart';
 /// reflector.
 ///
 /// This will also create .ng_deps.dart files for classes annotated
-/// with @Component, @View, @Decorator, etc.
+/// with @Component, @View, @Directive, etc.
 ///
 /// This transformer is the first phase in a two-phase transform. It should
 /// be followed by {@link DirectiveLinker}.

modules/angular2/src/transform/template_compiler/directive_metadata_reader.dart

@@ -15,8 +15,8 @@ DirectiveMetadata readDirectiveMetadata(RegisteredType t) {
 num _getDirectiveType(String annotationName) {
   // TODO(kegluneq): Detect subtypes & implementations of `Directive`s.
   switch (annotationName) {
-    case 'Decorator':
-      return DirectiveMetadata.DECORATOR_TYPE;
+    case 'Directive':
+      return DirectiveMetadata.DIRECTIVE_TYPE;
     case 'Component':
       return DirectiveMetadata.COMPONENT_TYPE;
     default:
@@ -101,7 +101,7 @@ class _DirectiveMetadataVisitor extends Object
     if (compileChildrenValue is! BooleanLiteral) {
       logger.error(
           'Angular 2 currently only supports boolean literal values for '
-          'Decorator#compileChildren.'
+          'Directive#compileChildren.'
           ' Source: ${compileChildrenValue}');
       return;
     }