Separate ringer volume from notification volume. One-year-old bug.

I do not want to hear bluetooth file transfer notifications, ever.
Currently, their volume is one and the same with ringer volume.
It's unacceptable. I have missed many calls because the volume was turned down for bluetooth - and the same volume is used for ringer, for unfathomable reason.
Hence, I would like to have separate volumes for notifications and ringer.

Hopefully, the changes made are suitable-working.