Simplified New Project dialog

@devoncarew

Use dropdown for the project type + a single checkbox for Polymer (downloads everything at once).

Additional project types are coming next.

![screen shot 2014-05-02 at 11 11 56 am](https://cloud.githubusercontent.com/assets/5606182/2866164/4b8f7988-d225-11e3-92b7-e3eff7357a4c.png)