ConquestiaMobs v1.3

Change Log:

- Added an unregister call to the disable method. Ensure all listeners
are shut down and reloaded on start up.
- Added new setting: “ExperiencePerLevel” to increase xp drop of
monsters.
- Added new setting: “startLevel” to have a preset start level of mobs
per specific spawn point.
- Fixed NPE with mob arena player list.