main-page-machines: pivot point is by default at 0.0, 0.0
main-page-machines: simplify the machine-view-size constants

In the long run, we probbaly want to sync this to the pixel resolution.
main-page-machines: improve zoom-fit

Remove commented/disabled code. Use the bounding box we already have. Clip the resulting zoom.
wire-canvase-item: adjust for renamed constants