Add biomegrid

Currently this PR does nothing else than filling the biomegrid, but it's a good base for terrain generator and biome decorators.

![far](http://i.imgur.com/wNrtA1A.png)

![medium](http://i.imgur.com/r9sO2et.png)

![close](http://i.imgur.com/jycyoW7.png)

**Related Links:**
 - PR: #572
 - PR: #580