Add a button to toggle sort order. Fixes #4

So, I've tried this wild backbone thing. I think I'll use it on my side, but maybe it could benefit other people as well :) Don't be too harsh, I am really not a "frontend" guy. In a better world, we'd have a little window for preference for this app, where we could set preferences like this one. To me, it's enough like this :)

If you're interested in having this feature, let me know if there are things I need to change.
Cheers