Page layout editor: Add bitmap items to the page layout existing items.
Now a bitmap image can be added to a page layout description. Currently the bitmap is expected having a 300 ppi definition.
Note: not all plotters can plot a bitmap, and in this case the bounding box is plotted instead of the bitmap
the spurious warning about stuff that couldn't be seen when changing
colours.
NOTE that the 'net name' layer is present and configurable but non used
anywhere!
* Correct all user strings and comments for the correct capitalization of
application names according to JP. They are KiCad, Pcbnew, CvPcb,
Eeschema, and GerbView.
* Add a note the the user interface policy about the correct capitalization.