- fix regression: allow grouping or not imported items
- store more settings in Pcbnew settings: all options are now stored.
- default tolerance to connect items is now 0.01 mm. 1 mm is a too big value,
and can create serious artifacts in imported outlines.
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.
