Add profile picture to menu

The whisker menu has always had the username, but it always felt like it was missing something... the user's profile picture! (located at ~/.face).

I have experimented a bit with adding the profile picture and it's starting to look pretty nice.
![menu](https://cloud.githubusercontent.com/assets/1431548/5330522/28186c36-7daf-11e4-9a39-814eae3556cc.png)

Feel free to let me know your thoughts and suggestions :)