WIP

This is the beginning of a UI migration. As I don't have the time to rewrite an entire Twitter app, I'm considering the rewrite of the UI small pieces by small pieces and React is a perfect library for it (and it can do XUL elements too!). If anyone wants to help, I'd be happy to merge into the next branch.

Let's go to immutability and composition!

For those who don't know about this talk, you should watch it!