Added an in-game map editor

I polished my ingame-map-editor branch for #3377 to allow the workflow of creating a blank new map, editing the terrain tiles and saving the map. Next is actor placement (at least spawn-/waypoints) and modifying the resource layer.
It looks nicer but causes glitches:

![image](https://cloud.githubusercontent.com/assets/756669/5564895/04899b06-8ed9-11e4-84ba-1e3b8b5a816c.png)

and is inconsistent when placing the actor which is what this TODO is about:

![image](https://cloud.githubusercontent.com/assets/756669/5564890/e0b70d62-8ed8-11e4-8026-8efbe172bf76.png)