Code review comment for lp:~artmello/gallery-app/gallery-app-remove_image_provider

I tried to reduce the delta between both versions of photo-metadata. But I don't think we can change the order of exposure time keys on gallery version of it. It is desired that when you import some photo into gallery it shows up in today's event, so when some new file arrives we save the date at Exif.Photo.DateTimeDigitized. When we are reading exposure time we should check this field first, otherwise we could use another date for ordering.