Feature improvment: Use exif properties to identify photos

[Sébastien Beausoleil]

Hi,

I restore the files folder of my OsmAnd app from my Nextcloud server (I use my server to automatically sync the app folder to make sure to always have a backup of my OsmAnd Data).  But, cause of some file manipulation, all the files modified/created timestamp have been change to the actual. Its causes some issues because the "name" of the photos seams to be link to the unix filesystem created timestamp.  I suggest the App uses the exif properties DateTime instead of the file creation timestamp, like it does with the gps coordinates embed.