Add review process for updates

Asset updates currently do not require a review. This includes images. Adding the review process might be hard because we have a state-based database, which means that "proposed" changes immediately end up in the database. The least invasive approach to add this is probably to add some kind of Json dump table to put the requests in, and have that reviewable and apply the changes if approved.

possible 'hotfixes' until then:
- [ ] disable updating image data after publication
- [ ] disable updating any data after publication
- [ ] allowing users to 'retract' their asset from published to draft, which would allow them to resubmit the edited asset. The asset would not be available in the mean time.