`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.
Added notifications on changing brightness, will stack by default to
show the current level before disappearing.
The script to change and notify can be run through the command
`control-brightness`, and is bound to the sxhkd media key shortcuts for
brightness changes.
Removed the brightness indicator from polybar since it should be easy
enough to check current brightness by doing a quick higher-lower and
that's it.
Kept the module in polybar configuration script since I might reconsider
its removal if it turns out to have been useful.
