Multimedia keys support

[AntoineTurmel]

Make a solid multimedia keys support for linux based on available add-ons and also check on how to use D-Bus on latest Ubuntu releases.

[freaktechnik]

+1

[Nowosad]

+1

[freaktechnik]

d92b4731195acfeec181baa1b8c87971422ba937 should add media keys support for most enviroments. It seems like there are no other APIs we can really use. But thanks to mpris it's easy to bind keys to functions now. But command line arguments for the ngale executable would be even easier.