Move cropping and texture and font rendering into CanvasRenderer

As discussed in

http://forum.movingblocks.net/threads/nui.869/page-2#post-9673

See here for an AwtCanvasRenderer:

https://github.com/mkienenb/Terasology/blob/review-engine-changes/engine/src/main/java/org/terasology/engine/subsystem/awt/AwtCanvasRenderer.java