Monitor the device reservation objects and mark the device available.
Don't select nodes from devices that are not available.
Acquire the device reservation when a device starts.
Release the device reservation when we suspend the device again.
Add a asprintf helper function that handles errors correctly.
Use this in places where we use asprintf to avoid warnings when we
don't check the return value.
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
