Improve search box positioning and styles

Moved search box outside TOC so that is stays on top when TOC is scrolled. Also styled TOC with Bootstrap's icons to make it look good.

This is how it looks in normal state:

https://www.dropbox.com/s/5fal92zui2zf45b/Screenshot%202013-12-12%2018.53.40.png

When you type a query, this is how it looks:

https://www.dropbox.com/s/6haswnx0lvmyiqm/Screenshot%202013-12-12%2018.54.01.png

Cheers!