Integrate power-profiles daemon

This allows to switch between the "battery-saver", "balanced"
and "performance" profiles.

It adds an action that can be configured to switch automatically
on AC (un)plugging or low power, as well as exposes that setting
on DBus for a future Battery Monitor UI.

Co-authored-by: Kai Uwe Broulik <kde@privat.broulik.de>