Add support for pulse client handling

[haasn]

This is a really cool tool, but it seems to be missing the IMO most important part of a pulse mixer: The ability to play around with individual client streams. (i.e. sink inputs / source outputs in pulse terminology)

Basically, I'm missing this tab from pavucontrol:

It needs the ability to

1. Change which audio device a program is playing on / recording from
2. Change the volume of that application

bonus points for also distinguishing between “applications only” and “all streams (including virtual streams)” like pavucontrol does.

[haasn]

Actually, disregard this. Upon closer inspection, it seems that pulsemixer covers this functionality: the individual applications are listed as “subitems” of the device they're on, and they allow movement as a context menu item. It seems I overlooked this when trying out pulsemixer.