Watch client object-manager and keep the remote source object in a
SourceProvider object. Keep a list of all sources in the daemon.
Handle the Client CreateSourceOutput by calling the method on a
registered source in the daemon.
Pass GDBusObject in the subscription signal so that we can get to more
details.
Rework subscription so that we can use it for client and server.
Move source and source-output to client to allow client provided
sources. Still needs some work but registration seems to work partly.
Rework DBUS API: move CreateSourceOutput to Client1 interface, remove
Add/RemoveProvider and Device1 interface. Rework SourceOutput1 to
allow for reconfigure.
Add a client to test v4l2 source.
