- first check CanControl property, as it overrules things
- next check each action Can* property, to spare D-Bus call and app activation if false
- support CanPause and only call PlayPause is possible, otherwise use Play
Vlc can be controlled by keyboard media keys as before,
Gwenview patched to support MPRIS (with CanPause=false) can now be
controlled with the Play/Pause media key.