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/test/transform/directive_metadata_extractor/directive_metadata_files/properties.ng_deps.dart

@@ -13,7 +13,7 @@ void initReflector(reflector) {
       'factory': () => new HelloCmp(),
       'parameters': const [const []],
       'annotations': const [
-        const Component(properties: const {'key1': 'val1', 'key2': 'val2'})
+        const Component(properties: const ['key1: val1', 'key2: val2'])
       ]
     });
 }