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.
Keep the client-source in the playing state for as long as the input is
streaming. Pausing the pipeline when there are no more readers causes
data to bunch up in the socket that gets bursted to new clients when
they connect.
Set the format on the client source when it is created so that other
clients can inspect the format. It also makes client sources show up in
the device monitor.
