Add the code to parse the properties of the media transport object when
a PropertiesChanged signal is received.
Note that the transport might have an owner other than BlueZ, and thus
the property changes would be emitted from arbitrary senders. For
performance reasons, the installed match considers the interface name
where the property has changed.
It could be possible to install and remove the D-Bus matches dynamically
when a new owner is registered/unregistered, but filtering based on the
interface name seems good enough already.