Implemented header top/bottom positioning via config

Hi @beardtree, really nice application! Thanks for creating it :) :+1: 

So I have implemented the functionality required for moving the header to the bottom of the application via the config (issue #7 ). What do you think?

![image](https://cloud.githubusercontent.com/assets/2520439/4060327/857d67ac-2dee-11e4-92a7-f19d8d0aad62.png)