Add Biome decorator

This is extensible and could help to implement the other things to decorate biomes with variations.
It already contains:
 - tall grass (and ferns but only in some biomes, so will be visible later...)
 - flowers and double flowers
 - sugar canes
 - dead bushes
 - pumpkins
 - melons
 - water lilies
 - cactuses

![grass and flowers](http://s4.postimg.org/7yeyz9ufh/2014_10_24_21_59_48.png)


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*Edited by turt2live*

**Related Links:**
- Ticket: #76