chat-manager: use tp_channel_join_async()
chat-manager: use tp_channel_join_async()

It's basically the same as empathy_tp_chat_join()

https://bugzilla.gnome.org/show_bug.cgi?id=675229

Distrotech/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets