Move Polymer about of labs

As discussed with @ebidel, I've added the latest version of the Polymer TodoMVC application to the labs directory in 895907666b3cc722afd5139c39396252f1ee9c88. Thanks to the Polymer team for their help with this :)

This issue is to allow us to do a code review of the app and check the implementation for spec-compliance. 

cc @passy @sindresorhus @stephenplusplus from our side and @sjmiles @morethanreal from Polymer.