* Implemented 2 new battleground commands. Closes#1531.
* bg_join - join battleground without npc chat room
* bg_create - create a battle group without npc chat room
* Made events for bg_create and waitingroom2bg optional
* Made map,x,y parameters on waitingroom2bg_single optional
Thanks to @Lemongrass3110 and @cydh for code reviews
Thanks to @aleos89 for documentation cleanup