waveform drawing details:

* proper y-pixel alignment (+.5px offset)
* outline: draw dots (not 1px lines)
* shape: round towards peak (use signal, not top/bot)
* honor 2px red selection border
* work-around canvas rect +1 issue
* always draw clipping line towards center
* draw at most one clip-line at either side of 0.
* exact 1px wide zero line
* fix spread calculation for rectified view
NOOP, remove trailing whitespace
don't clamp wave-fill alpha value when using region color
reasonable dB range for waveform clipping indicator