Insert 'FLAT' or 'NO_TARGET' in image types with no target

[Ben Cartwright]

This could be images produced from the Flats wizard or other sources, to allow them to be saved as expected when the image path has \$$TARGETNAME$$\ in the path, as opposed to the folder tree being skipped entirely as it is now.

[Ben Cartwright]

To be more specific - set the Target Name as ‘FLAT’ or ‘NO_TARGET’ in this scenario

[Stefan B]

flat wizard has a custom target name option.