Consoles

This adds a new level to the navigation stack. It separates out roms into their own Consoles so you can browse by console.

Kart now starts by showing you a list of your valid consoles, picking one will show you it's roms, and pressing `ESC` will bring you back to the list of consoles.

Console images are set by adding a banner image named `image.png` to the console's directory.

![consoles](https://cloud.githubusercontent.com/assets/260/3008123/bffb4dd4-deae-11e3-8b2f-45766de6bd25.gif)