gnome-volume-control: add profiles

[Peter Woulfenberg <woulfenberg gmx net>]

Hello GNOME Lovers,
I'm not sure, if this is the right place to make a feature request, but 
I didn't find anything for this on the homepage.

It would be very nice, if you could create different profiles in volume 
control. I have a 7.1 set-up and there here are some use cases:
- Profile 1: Sitting in front of the computer, listening to music (more 
on rear speakers)
- Profile 2: Sitting on the couch, watching a movie (less on rear 
speakers, more on the center)
- Profile 3: Being in the shower, listening to music (only one side 
speaker active)
- Profile 4: Being in the kitchen, listening to music (more bass)

Of course the user should be able to save his own profiles.

Thanks for your time and happy hacking :)
Peter