remove orange frequency toggle buttons
frequency controls in a grid
frequency controls: use QDoubleSpinBox
connect step size dropdown
embiggen QSpinBoxes, arrange 2x2
frequency control: use embedded suffix
remove span calculation from frequency controls
compute span in controller, not frequency controls
no reason to disable labels
disable frequency controls on playback
update changed list in controller if span changed
fix for initial None state
Plot.user_xrange_change signal
user xrange control (Auto mode)