support Statuses on TpConnection
Submitted by Danielle Madeley
Assigned to Tomeu Vizoso
TpConnection should expose the Statuses property.
< smcv> danni: once we have the basic API for Features, the handling of
Statuses can be cargo-culted from tp-qt4, where "SelfPresence"
(statuses + the current value of my own presence) is a Feature