UI + project template to add bower.json with Polymer/custom dependencies to main templates

@umop. @dinhviethoa

This is a part of the ongoing merge/development of Bower support.

Selecting one of the new checkboxes in the New Project dialog ("Polymer core", "Polymer elements", "Polymer UI elements") or entering properly formatted dependencies in the "Additional dependencies" text box will pull the properly filled-out bower.json and the bower_packages directory into the base project selected under the "Project type".

This is a work in progress to some degree. I'm planning to extend the set of templates to address #1474 and #1475, and possibly make the templates more orthogonal to minimize the overall number (e.g. move pubspec.yaml out of Chrome App so that Pub dependencies could be applied to any project type; etc.).

![screen shot 2014-04-03 at 10 58 21 pm](https://cloud.githubusercontent.com/assets/5606182/2612280/58eccaea-bbbe-11e3-977d-2fcf3e242923.png)