Implemented remaining entity type methods in GameRegistry.

* Updated API.
* Minor fixes.
Add villager implementation. Merges PR #95
Add WorldBorder implementation. Merges #89
Implement PrimedTNT. Merges #96
Implement ExperienceOrb. Merges #97
Return immutable lists in registry where applicable.

* Removed unneeded blank lines in MixinEntityPlayerExample.