pulse-server: Implement module load and unload
Implement a minimal version of the LOAD_MODULE and UNLOAD_MODULE stream commands. The only supported module for now is the null sink.
Modules are stored on a per-client bases, so that when clients are disconnected, the modules they loaded is removed too.
This is enough to allow GNOME Network Displays to register a sink.
Edited by Wim Taymans