Completed basic motion logic

Completed the basic logic for gliding, ground movement, jumping, crouching, and transitioning between these states. Right now crouching doesn't actually do anything except set a flag.

I also added a new material type to remove friction from walls - I changed the DirtTile prefab to use this material but we'll need to use it for future materials too (if we plan to have them as walls).

I've also created a new layer called "Ground" that is used for ground checks - please make sure to add future tiles to this layer (I've already added DirtTile to it).

Removed the old GlideTestScene, please use LevelGeneTest scene instead. I left it the same, except added the sprite to it.