* cpu+memory: Open "gnome-system-monitor"
* disk: Open nautilus
* pulseaudio: Mute/unmute, open "pavucontrol" on right-click, raise/lower
volume on mouse wheel up/down
Pass the "output" object to the modules' constructor to allow them to
define their own callbacks.
Any user-provided callbacks take precedence and override those of the
module.
Add a module that retrieve mute status and volume (left, right, mono)
from pulseaudio. Unfortunately, this module is really, really hacky. It
invokes "pactl" multiple times to get the status and does some ugly
parsing on the output.
Overall, this is pretty brittle and prone to failure, but as I was not
able to find a decent pulseaudio library for Python... Probably, I
haven't searched hard enough, cannot believe such a thing does not
exist.
