Show a list of the user's Firebases (including auth tokens)

I thought it would be nice to see a list of the user's existing Firebases under the url-input, so that you don't have to copy and paste everything every time you want to use vulcan.

Since this is the first time I have ever touched ReactJS and Chrome extensions, I fear my code is rather messy. I welcome any cleanups or additions :)

Ideas:
- [ ] make it pretty
- [ ] make the list clickable (and prepopulate the inputs; I might dive deeper into React in the next days)
- [ ] check if user is logged in on firebase.com

![comparing_firebase_master___lukasklein_master_ _lukasklein_vulcan](https://cloud.githubusercontent.com/assets/1492869/5194412/03812016-750d-11e4-8e11-59ddfc15c388.png)