fix(scope): fix $properties not visible using []
fix(scope): fix $properties not visible using []

 -Fixed broken containsKey.
 -Refactored operator[].
giovannicandido/angular.dart,SibuStephen/angular.dart,rkirov/angular.dart,trinarytree/angular.dart,hitesh97/angular.dart,winstonewert/angular.dart,SibuStephen/angular.dart,trinarytree/angular.dart,winstonewert/angular.dart,winstonewert/angular.dart,ronlobo/angular.dart,hitesh97/angular.dart,rkirov/angular.dart,ronlobo/angular.dart,giovannicandido/angular.dart,ronlobo/angular.dart,rkirov/angular.dart,winstonewert/angular.dart,rkirov/angular.dart,hitesh97/angular.dart,hitesh97/angular.dart,ronlobo/angular.dart,SibuStephen/angular.dart,giovannicandido/angular.dart,trinarytree/angular.dart,SibuStephen/angular.dart,trinarytree/angular.dart