Cleanup some dead code
Move some functionality from VisualPitchDetectionNode into parent class
Add rounding to key bins when isolating peaks

Sometimes, it's impossible to find a tuning that will get all of the
fretted notes in key bins (bins containing idealized concert pitches),
because of imperfection in the instrument or strings, so it's necessary
to round peaks to the nearest key bin neighbor to make the instrument
usable by the app.

I found this was the case on a Yamaha Pacifica 112J with DR Pure Blues
10-46 electric guitar strings.