And place bitmaps behind other items. This ensures they are drawn in
the background of the page rather than covering schematic elements.
This also hacks around the buggy wxPostScriptDC implementation that
resets the page to print an image.
Fixes: lp:1819934
* https://bugs.launchpad.net/kicad/+bug/1819934
When selecting the "Print in B&W", all items on the schematic should be
printed using black and white. This converts the embedded images
greyscale before outputting to the printer