Make arenaManager static

There can be only one
Fixed join command not properly parsing teams
Added method to arena to (re)load config values
Renamed onPlayerDamage to onPlayerDamageByEntity
Renamed playerjoin and playerleave + check config

Now called savePlayerConfig and loadPlayerConfig
Also added a check to see if a certain value exists in the config, this
should prevent errors from being thrown incase a config wasn't properly
saved
Refactor to follow ArenaPVP &ArenaManager changes

ArenaPVP is now a singleton class, instance can be retrieved via
ArenaPVP.getInstance()
ArenaManager is now a static class, every method and variable has been
made static to ensure there is only one arenamanager at any given time
More commits to properly change the code to use these changes may
follow, all major refactoring necessary to make the code compile
properly has been put in this commit