tp-chat: set Private and InviteOnly props on conference channels
tp-chat: set Private and InviteOnly props on conference channels

Only the person invited are suppose to join these channels so tweak their
settings to make them more secure.

https://bugzilla.gnome.org/show_bug.cgi?id=684675

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