Add some data to images to follow metadata updates

[gdozot2]

It would be interesting for owners to know when the metadata associated with an image was at latest updated.
For instance, after an owner exported all the data of a collection, it could be interesting to know a few months later if new corrections or computations have been done and some data need to be updated (without performing a full synchronization).
At minimum, could be good to add a date_updated (or date_metadata_updated), could also be split by type:

date_georef_updated
date_viewshed_updated
date_toponyms_updated

date_metadata_updated (title, description)