That app was called GEDitMobile and it was very compatible with GEDitCOM II including import of thumbnails of images (I worked with the developer), but it is no longer available. Unfortunately, it was written by some old iOS methods. The developer has recently started to convert to new iOS (using the Swift language) and it might reappear. His first goal is to have a full read-only copy so you can carry your data on your phone, but editing would done on computer in GEDitCOM II. If there is interest, some editing options might be made available later with the goal of making round trip data transfers 100% accurate.
Any status changes will be posted on this group.
Regards,