scripts: Add unified volume bars to control scripts

`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.

scripts/.local/bin/control-volume

@@ -54,13 +54,16 @@ send_notification() {
   fi
 
   vol="$(get_volume)"
+  bar=$(seq -s "─" $((vol / 5)) | sed 's/[0-9]//g')
+
   if [ "$vol" -eq 0 ] || [ "$(get_mute)" = "off" ]; then
     # Show the sound muted notification
     $notcmd -a "changeVolume" -u low -i audio-volume-muted "Volume muted"
   else
     # Show the volume notification
     $notcmd -a "changeVolume" -u low -i audio-volume-high \
-      -h int:value:"$vol" "Volume: $vol%"
+      -h int:value:"$vol" "Volume: $vol%
+$bar"
   fi
 }