Finished the stat system.

- Mappacks can register their stats in a file called 'stats.cfg'
- The stat emitter has different modes. Normal, Inverted, Pulse on enable, Pulse on disable, pulse on change
- Custom stat types can be registered by subscribing to the RegisterStatTypeEvent
- Custom stat tiles can be made by implementing IStatTileEntity and posting StatTileEntityEvent.Load on load and StatTileEntityEvent.Unload on unload