v4: Battle annoyingly over-specific css selectors in grappelli
v4: Usability improvements to upload popup
v4: Render standard ImageField for non-imported values

If an instance's CropDusterField has an image path on that model
(making it compatible with the original ImageField) but does not
have a corresponding row in cropduster.Image, then render the
standard ImageField and widget.
v4: Number of bug fixes, pre-release status