feat(Directive): convert properties to an array

fixes #2013

BREAKING CHANGE:

Before

    @Directive(properties: {
      'sameName': 'sameName',
      'directiveProp': 'elProp | pipe'
    })

After

    @Directive(properties: [
      'sameName',
      'directiveProp: elProp | pipe'
    ])

modules/angular2/src/directives/ng_if.ts

@@ -27,7 +27,7 @@ import {isBlank} from 'angular2/src/facade/lang';
  *
  * @exportedAs angular2/directives
  */
-@Directive({selector: '[ng-if]', properties: {'ngIf': 'ngIf'}})
+@Directive({selector: '[ng-if]', properties: ['ngIf']})
 export class NgIf {
   viewContainer: ViewContainerRef;
   protoViewRef: ProtoViewRef;