Extract pkg cmd abstractions and clean up all migrations (#1291)

* No using custom chromium.desktop any more

* Spacing

* Rely on $OMARCHY_PATH

* Add common pkg and cmd functions for use in migrations and elsewhere

* Simple pkg-adds

* Later migration does it

* Ensure running migrations on older installs have the new pkg/cmds available

* Spacing

* Use new abstractions

* Installed in later migration

* Needless comment

* Use new commands

* Fix package name from 'batt' to 'bat'

migrations/1752725616.sh

@@ -1,4 +1,5 @@
 echo "Make light themes possible"
+
 if [[ -f ~/.local/share/applications/blueberry.desktop ]]; then
   rm -f ~/.local/share/applications/blueberry.desktop
   rm -f ~/.local/share/applications/org.pulseaudio.pavucontrol.desktop