New Linux download page

@tresf 
Made the linux distributions tab-switching and added the ditros' logos using a custom icon font I quickly made here: https://github.com/Lukas-W/font-linux | http://lukas-w.github.io/font-linux
What do you think? 

![image](https://cloud.githubusercontent.com/assets/2879917/3854998/29bab938-1edf-11e4-97ed-6a2fbb75f2df.png)