iOS app: saved images do not have time set in EXIF

When saving images from the app, the EXIF “Date/Time” tag is not set. This would be great to do, allowing images to be properly ordered in JOSM, for example.

Practical workflow: taking images for mapping (because Mapillary queue might be too long, or because it could blur flat numbers or other data), saving them to be used in JOSM, while originals get uploaded to Mapillary in parallel.

@Anders did you want to chime in on this one?