Add a entry/exit flag that ignores teleporting

WORLDGUARD-3078 - Reported by TGS

Sometimes you want a place where people can't exit from (could be a Hunger Games arena etc) but you want them to be able to leave using other plugins (/warp, /spawn, /hg leave, /leave etc.) by teleporting. Therefore it would be useful to have a exit + entry flag that ignores if plugins teleport people out and only prevent it if they walk out.