new graphics settings and better performance

added two new graphics settings:

• terrain detail: affects distance at which the terrain is rendered at full quality
• render distance: a heavy-handed way to gain performance by simply rendering less (fun-fact, this is the same method the original web-browser version of the game used in order to run at decent framerates)

also rearranged the level-select screen such that level 2 is on the left. the reasoning for this is that i think level 2 is a better staring point than eraser classic for new players, and this layout better reflects that.

also fixed a bug that was prevening the planes from tinting properly in level 2.