Add browse rooms button in join groupchat dialog. Fixes #3546

don't show sign in/out notifications if another resource or a metacontact brother is already connected. Fixes #5318

fix insecure_connection text to not talk about password, and add new warning to inform user when he is about to send plain password on plain connection. Fixes #5607

prevent traceback when destroy handler already clean self.instances[account]['online_dialog'] dict. Fixes #5604