MantaMIDI feature request - function buttons should have alternate functions

[spiricom]

it would be great to have a checkbox in the GUI that allowed for another state, where instead of sending notes, the function buttons would do one of two things:

1. change octaves up and down
   or
2. change the sliders, as in our manta max patches.

Number 2 would obviously be more involved -- you'd have to save the state of the sliders internally in MantaGUI and update the LEDs based on the saved states.