[Enhancement] "photo area" / object based tags

[qwerty287]

Explain in a few words which functionality or improvements you would like to see in Lychee.
I would like to be able to assign tags only to certain areas of a photo. E.g. to mark objects in a photo, a prominent use case would be face tagging. Also, an overview about all tagged areas and photos would be very nice.

[ildyria]

While I do like the idea, this requires a significant chunk of code to be added.
We are currently in the middle of a huge refactoring ( #1217 ) so I would suggest to wait until it is merged to start working on such project.