Add hidden settings to the GUI

Basically #2687 without the game speed slider and rebased onto current bleed.
![video-settings](https://f.cloud.github.com/assets/756669/240899/5fba7404-895f-11e2-8ca6-1ef4cc503de2.png)
![audio-settings](https://f.cloud.github.com/assets/756669/240898/5df97b56-895f-11e2-81e4-41251c1cc103.png)
![debug-settings](https://f.cloud.github.com/assets/756669/240900/6124c6dc-895f-11e2-8c22-dcf38aab657c.png)