Removed no-longer-required differentiation between importing
footprint vs board objects.
Renamed files to match the dialog.
Made Position At and Set Layer optional checkboxes.
Removed Group Items checkbox. (In the unlikely event that you don't
want a group, do an UnGroup after importing.)
Flattened out labelled-sizers in the dialog.
Removed importers blacklist, which hasn't been active for at least 4
years.
Fixed undo/redo bug that caused items to be no-longer-grouped after
a redo.
* Fix wildcard display in the file selector dialog (on GTK
it would show the regex to the user)
* Move the file extension comparison into a common function
The returns of KiCad file extensions on GTK contain basic regex matching
case-insensitive file extensions. We need to match these in the
provider and tests