Panel userlist live search

Related card: https://trello.com/c/zqzlkjJf

This patch adds live filtering capabilities to the user list in the panel:

![screen shot 2014-02-11 at 18 19 34](https://f.cloud.github.com/assets/41547/2139592/c0a5fdb0-9340-11e3-87c6-64c0a1608643.png)

**This is ready for review.**