Optimization: added methods getPlayersUUID, getOnlinePlayersUUID and getSize to UHTeam (#58).
Optimization: now using a Set to store players inside a team. (#58)
Optimization: now using a Set to store the registered teams.

Added a method to chec if a team is registered.

Updated the code to follow these changes. (#58)

Real fix for the UHGameEndsEvent being called multiple times.
Optimization: updated the code to use the isTeamRegistered methods. (#58)

Fix: fixed team-teleportation not working with some players in the offline (NPE).
Fix: fixed team-teleportation without the UHTeam.teleportTo method.
Optimization: the alive teams are cached. (#58)