Add support for enabling or disabling actions programmatically

This series introduces the concept of actions being default to enabled or disabled and adds an API that allows users to turn on/off the actions.

To avoid confusion with projects using the legacy interface the new API is only present on the modern interface.

This also changes the panel_power_savings action to default to disabled. Users will have to re-enable it using powerprofilesctl configure-action panel_power_savings --enable or by using the matching new dbus interface.

The preferences of a user will be saved into the PPD configuration file and used for configuring PPD the next time it runs.