Add instrospection of client and source-output.
Add properties to source-output and to CreateSourceOutput/Input
Add helper to fill properties of context.
Add client-name to pinossrc and pinossink
Improve test-subscribe to show all new introspection details.
Set the active device providers as a property on the daemon. In the
device monitor we can then obsolete the already monitored devices.
Copy all device properties to the source. Set the device class as
a property on the monitored devices.
