Add some vanilla structures

This PR will add some vanilla structures.

Work done:
 - Witch Hut
 - Dungeons
 - Desert Well
 - Jungle Temple

The current implementation supports cancellation like trees for a possible future support of a StructureGeneratedEvent in GlowKit.

It should be noted that this PR is only based on building these structures, some structures like the witch hut or the jungle temple will need a nbt storage file and a structure mapping (this allows to place them in the terrain generation and not on the chunk population phase in order to have clean undecorated terrain to place the structures on) but this will be part of another PR.

![DesertTemple](http://s1.postimg.org/5rqb4gea7/2014_11_16_09_52_29.png)

![WitchHut](http://s28.postimg.org/icgutb9el/2014_11_16_09_52_49.png)

![JungleTemple](http://s21.postimg.org/5s9ys4o7b/2014_11_16_09_55_31.png)