add a new project fab button

- added a `New Project` material design FAB button to the UI
- added a reference to the JavaScript Polymer material design components
- added some command infrastructure, which can map string command names to command handlers. Also, commands can optionally be dispatched through the DOM

![screen shot 2014-10-07 at 2 01 41 pm](https://cloud.githubusercontent.com/assets/1269969/4566477/8a9c87d4-4f29-11e4-885e-d006db5660eb.png)

@ussuri, @rginda. Rob, I'm hoping that the command stuff here can migrate towards the JS infrastructure, when it's available, and that this could be a dart interface to that.

For future (not this CL), perhaps we'd want to move this outside `/ide/web/lib` into a new `/cde-commands.dart`: I think this is a prime example of a useful generic module that doesn't need to be integrated in the IDE itself.