Add guard at top and bottom of range when deadbanding

* This is important to get true intervals for the pitch wheel, because
  the analog voltage from the wheel as seen by the ADC is not the
  whole available range, leading to the resulting output from the ADC
  not to cover the whole 0..65535 range.
Use struct for deadband configurations
Added newline at end of ui.c
Precalculate band calibration scale factors

* Also clean up UI call to update bender when calibration changed
Cleanup
Decrease bend deadband and guardband slightly

* Initially set values seemed unnecessarily large