Polymer Designer code "as is"

TBR: @devoncarew 

In preparation to checking in the CDE Polymer Designer feature, this is a direct copy of the PD repo with downloaded dependencies: nothing much to review here.

If at some point we manage to incorporate Bower into our build process, it will become possible to automate downloading of PD and its dependencies, so none of this will have to be in our repo. One possible option is to make our  Bower implementation fully featured, and available as a standalone package. Then we can download and run it inside grind.dart.