new feature: page through sets of (4) samples using select/start buttons

[hunterirving]

the four drum hit locations (left outer, left inner, right inner, right outer) should map to the default MIDI notes for FL Studio's FPC plugin's top row of pads (C#4, G4, D#4, F4...?) and page into the next row when START is pressed

this will eliminate the need for manually linking notes to samples
and give us 4x the amount of samples to play with