Add Vaadin Elements to Demo Kitchen Sink about origami

[hotforfeature]

Pushed an update to the vaadin branch that has <vaadin-grid> working. Only thing that's wonky is two-way databinding for the select all checkbox, and that's part of a bigger issue with Angular properties getting bound to Polymer templates that I created #36 for.

If you're watching this issue for vaadin support, most elements that I've tried work naturally. The grid will depend on vaadin/vaadin-grid#890 getting merged, so subscribe to that if you're looking for grid support.

This issue will remain open for a little while since I'd like to clean up the demo project and organize it better.

[hotforfeature]

Vaadin elements are present in the demo, just waiting on the above grid issue to be production ready. Going to close this and create a new issue later to clean up the demo app.