Per-player Boss chests and bug fixes

Fix issue with gamepad allowing navigation behind current UI panel
Fix video mode thrashing when changing settings
Fix invalid sessions not being properly removed from the open party list
Fix issues with abilities damaging friends and/or not applying positive effects on friends
Loot rules now visible to all players
Boss fights now spawn chests for each player
Fix invalid Meteor strike hit location
Fix channel abilities preventing death animations from playing
Enemies that spawn from pods remain complete after players leave and return the the area