Metadata allows apps to attach properties to objects that can be
read by other apps.
Not complete yet, properties should be removed when the object is
removed.
Change node.priority to priority.session to indicate that this
is the priority that the session manager uses to select the node.
Add another priority.master that the core uses to select a master
driver. Keep the driver nodes sorted by master priority.
Let jack always prefer to connect to the master driver nodes.
Add a jack device and activate it when we release the device (for JACK
presumably). We need to work around some issues, jack does not allow
us to connect yet when it asks to release the device so we need to
wait a little and then connect.
Implement the device reservation DBus API.
When we acquire the device name, set our device profile to 'On'. This
adds our sources and sinks to the graph.
When we lose the name, switch back to 'Off' and remove our nodes
again.
Move the session mamager stuff in a directory.
Fixes#191
