Jingle Message Initiation is currently not useful for components, and the message workflow
is different in Libervia between clients and components (as a result, `messageReceived`
trigger is never called, and the session proposal is never answered).
This plugin uses the new `XEP-0166_initiate` trigger to initiate a Jingle session with
messages if the peer jid has no resource specified.
On reception, if the sender is not in our roster, a confirmation is requested to user to
avoid leaking presence and IP. If user refuses the session for somebody not in roster,
nothing is sent at all (the request is just ignored).
