Add water plant objects. Improve grass texture.

Improve grass texture:
![image](https://cloud.githubusercontent.com/assets/1470603/3561241/d9a21708-09b1-11e4-9f10-5a1828982cd9.png)

Add water plants:
![image](https://cloud.githubusercontent.com/assets/1470603/3561247/2167df28-09b2-11e4-84b4-3424042a8ac7.png)

TODO later (by lionleaf?):
Do something with the water plants in doom (burn them?)