Expand the KCM to generally manage application permissions

This transforms the kcm from a very technical thing that manages knobs of the flatpak sandbox to one that manages app permissions via the permission store. The flatpak settings are still available as is for flatpak applications.

The review is split between three commits to make review a bit easier:

• The first commit adds the new code
• second commit integrates the old code again
• third commit does boring, renaming the kcm and adds a new readme