Add permission based access to warzones

Adds a team default permission configuration option. Default is
war.player. It is modifiable at the zone level and the team level. In
autoassign zones where there is a mix of teams that some players have
access to and some that they don't, the player will only ever be placed
in a team he can access. You can't /join a team you don't have
permission to join.
Merge pull request #579 from cmastudios/zone-permissions

Add team-based permission requirement