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.
Add introspect API
Move private things to private.h
Use custom main-context for the context, and ensure everything is called
from the custom main-context. does not work well with glib proxy signals
yet.
Work with custom mainloop in the gstreamer element.
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.
