This attempts to fix performance when importing large changesets from schematics.
The appearance control is a BOARD_LISTENER that would otherwise redraw per item imported which may cause lockups
It shows much more detail. Removes some nag dialogs and places
hypertext links in others.
Also fixes the auto-layer-showing to correctly show Edge.Cuts or
F.CrtYd or B.CrtYd for errors relating to them.
Fixes https://gitlab.com/kicad/code/kicad/issues/6446