Map objects

Adds some nice toys for mappers.
Spawners and nests for now, very simple stuff.

Also some sprites that aren't big red X's:

![image](https://cloud.githubusercontent.com/assets/6355724/4262879/ef10355a-3bbd-11e4-9ecb-eb4fc1620b31.png)

![image](https://cloud.githubusercontent.com/assets/6355724/4262880/f3a72f24-3bbd-11e4-9eab-ba5a5077a1c3.png)

Everything's tested and working fine as far as I can tell.