Fixed plugin command registration.

* Fixed plugin container lookups.
* Fixed getPlugin(id).
* Fixed wrong super in MixinEntitySnowman.
Add basic support for PlayerJoin/PlayerQuit events.

The underlying events are fired at a bad time for messing with the messages,
so that is not supported yet.
Implement basic MessageBuilder
Make the license plugin consistent with SpongeAPI
Implement Title API
Update mixin submodule
Added support for executing plugin commands.

* Minor cleanup.
Updated API
Implement getTranslation for MixinBlockType and MixinItemType.
Merge pull request #84 from Hidendra/feature/type-translation

Implement getTranslation for MixinBlockType and MixinItemType.
Update Forge version for performance fix
Cleanup prefixes.
Add missing @Override annotations
Add MixinEnchantment
Fixed IRC raised issues
Fixed table troubles
Fixed getId not working
Fixed so everything works
Fix current mixin examples so they compile
Change namespace of mixin examples to match the real impl