Managing contact information, commonly known as the "roster",
is a big part most clients. This includes handling things like a contact's
real name, presence and status, avatar and client capabilities.
A list of handles usually comes from a channel with the
Group interface (i.e. a chatroom
or a contact list).
In general, a client will connect the relevant signals to receive updates
for presence, aliases, avatars, capabilities, and so on; and then use
the Contacts interface to
bulk request the intial state.
