making XmppRoom handlers instance fields rather then class fields

this fix is about making handlers stored in each XmppRoom individually for not notifying all the rooms about presence or message happening in one of them.
this patch is very small (coffeescript part, about js - i don't understand why does it differ so much) and i should have taken care of _handler_ids, but for now i would like to know your opinion on this kind of change - maybe i misunderstand the idea behind this kind of handlers storing
thank you