Fixed an error with updating a multi-image field

Without this fix, if a field had eg. 5 photos and one more was added,
only the added one was saved - because photos, that were not moved from
the temp folder or matched some other condition were not added to the
saved list of pictures.
Fix allowing ImageField objects be moved to the permanent folder

Without this fix images stored in the ImageField were never moved to the
permanent folder - if i get it right, the ImageField class was just
ommited here by mistake.