Frontend-GNOME-XMPP: AddChatState function name did not represent what the function does
Engine(-XMPP),Frontend-GNOME-XMPP: offline/away/available messages don't make much sense in private chats

added PresenceStateAway and PresenceStateOffline to be able to filter them in the frontend and display as presence states instead (only one presence state is ever displayed). PresenceStateAvailable removes all chat and presence states.