Pass GError around for things that can fail and report the errors back
to the client.
Improve shutdown of pipeline when no clients are consuming.
Make GStreamer elements handle all kinds of data and not just video
because we can.
Use generic byte blobs for formats. We currently use them to store
gstreamer caps but we could also use them to exchange serialized
GVariants if we want.
Make properties a variant dictionary
Move source and source-output to the server side again.
Make the daemon track objects per sender so that we can remove them
when the sender disappears.
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.
