This is a highlevel library for working with xdg-app without using
the commandline interface. The primary usecase for this is for
creating a graphical frontend for app installation/update.
This moves a all source code into separate subdirs per binary. The
helper and the generic stuff goes into lib/ which is then used by all
the others. For now this is a completely internal library, but at
some point we will probably clean it up and expose some subset.
Also, we move the dbus proxy to libexecdir.
This is a small app that makes copies of various system files to a directory
in /run so that the app sandbox can receive updates to these. This solves
the issue that we can't generally bind-mount say /etc/resolv.conf, because
it will be replaced with rename-over.