The inhibit dbus call to gnome sessionmanager expects flags as input.
Currently the flags are set to 4, which will "Inhibit the session being
marked as idle". This is insufficient to prevent the device from
suspending while playing.
We should also add 8 = "Inhibit suspending the session or computer".
Hence, the updated flags to 12.
This change was tested on phosh/phoc and it properly prevents the
system from suspending. The flags = 12 settings is also what gnome
music players like Lollypop are using (as checked through the gnome
sessionmanager dbus interface).
Both classes are based on classes taken from Elisa.
The audiomanager class will be adapted to add functionality like saving
and restoring play positions and interfacing with MPRIS2.