Fixed RSM in room discovery.
Split mod_muc_room:destroy_room/2 into a set of functions.
Split mod_muc_room:process_presence/4.
Split mod_muc_room:add_new_user/4.
Prettified mod_muc_room:set_opts/2.
Rewrote get_mucroom_disco_items.
Split mod_muc_room:check_invitation/4.
Fixed bugs.
Merge branch 'arc-muc-rsm' into arc-mod-mam