directly apply waveform clip-level changes
persistent waveform shape setting.

NOTE: the call to set_global_shape() only needs to happen once,
presumably in a hook in the editor that catches Config::Changed

The same is true for waveform-scale and clipping. But for now it's
at least consistent.
global one-time setup of waveform preferences.

see note in previous commit.
implement Curve in/outside fill
x-fade drawing rework, part one