add license note to all live examples

[petebacondarwin]

All of our live examples (codepen, plunkr) must include the following statement at the end of each file:

Copyright 2016 Google Inc. All Rights Reserved.
Use of this source code is governed by an MIT-style license that can be found in the LICENSE file at http://angular.io/license

I have the license hosted on angular.io, but you could point to a more angularjs-specific hosted copy if you prefer. It doesn't matter -- the text for all our licenses is the same.

(Copied from angular/angularjs.org#184)