#148 Move sound peripherals into separate submenu

[Arki55]

Move following perihperals:
- Melodik
- Fuller Box
- Specdrum
- Covox
- D/A Converter (see separate ticket)

into separate submenu under "Peripherals/Sound"
+ move their .c and .h files into new folder peripherals/sound

Implemented here

Branch:
https://sourceforge.net/u/arki55/fuse/ci/arki55/features/T4-sound-peripherals-menu/~/tree/

With D/A Converter:
https://sourceforge.net/u/arki55/fuse/ci/arki55/mixes/T2-T4/~/tree/

Pull Request back to Fuse:
https://sourceforge.net/p/fuse-emulator/fuse/merge-requests/14/
(only the standalone feature - T2-T4 mix on request)

See also
https://sourceforge.net/p/arki55-fuse-mod/tickets/4/