This interfaceifies the extra functions that were on GDBusActionGroup
for dealing with platform data.
The two main benefits of doing this:
- no longer have to do a silly song and dance in GApplication to avoid
calling GDBusActionGroup API from non-dbus-aware code
- the interface can be reused by the action group exporter to avoid
ugly and unbindable hook callbacks
https://bugzilla.gnome.org/show_bug.cgi?id=665737
