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/transform/common/directive_metadata_reader.dart

@@ -56,7 +56,7 @@ class _DirectiveMetadataVisitor extends Object
     meta = new DirectiveMetadata(
         type: type,
         compileChildren: true,
-        properties: {},
+        properties: [],
         hostListeners: {},
         hostProperties: {},
         hostAttributes: {},