GSettings: Actually, there was still a GConf PTRACE.
VideoInputCore: Fixed possible deadlocks on exit.
Opal: Fixed missed call signal emission.

When the call fails because there is no common codec (or any error that
prevents the call from being established), we had a missed call signal
emitted and a nice deadlock.

Things are now correctly handled.
Opal: Fixed objects initialisation.

We still need to rely on a public setup method to define initialisation
order.

Otherwise, the OpalCallManager could emit the "ready" signal (indicating
it is ready to process calls and registrations) before other objects had the
time to connect to it.
X11: Fixed black window problem when displaying video.