amixer mutes all individual output streams when it mutes (master,
speaker, headphone) but only unmutes master by default.
This is a simple fix to unmute everything when we do.
`control-brightness` and `control-volume` both now have the exact same
progress bar indicator.
Additionally, by using the same dunst 'stack' they replace each other if
invoked in quick succession, which I really like.
`pavolume` was nice, but my own volume script is just more flexible. No
real changes yet, but includes notification through dunst and works the
same way as `control-brightness` script does, just invoked through
`control-volume`.