svgui

Remove debug output

Use ScaleTickIntervals (which postdates WaveformLayer) to get sensible scale points for the waveform vertical scale, in linear mode at least (no change to the other modes)

A crude effort to fix the incorrect measurement crosshairs on retina Macs in the spectrum layer. This gets the x coord right, but the y coord is still wrong. (The root of the problem is that most content is rendered expressly to an image at retina resolution, but the crosshairs are rendered at interaction resolution afterwards, so they have different coordinate systems)

Restore spectrum vertical scale to the visual extent it had before root-power fixes, by doubling the numerical extent when showing a root-power quantity