Add a compact friends list layout

When the friends list gets large, you can't fit all your online friends on it anymore, which gets annoying, so I've written a compact layout mode for the friends list.

Here's what it looks like:
![scrot-757](https://cloud.githubusercontent.com/assets/290001/5395391/c8444f62-8148-11e4-919a-9a7a8afa8d5a.png)

The only problem there is, I think, is that when you check/uncheck the compact layout checkbox in general settings, the friends list layout won't reload and you need to restart qTox for the changes to have any effect. I'm not sure how to fix this. If anyone can point me in the right direction, I don't mind fixing this.