This commit introduces the notion of "effects profiles", with
reverb/chorus settings that can be set on a per-SoundFont basis.
The configuration file has been updated with an example of applying a
profile to the GeneralUser GS SoundFont.
This commit adds a simple physical control system with two schemes:
* simple_buttons: 4-button scheme
* simple_encoder: 2-button scheme + rotary encoder (with button)
