Developed from comment to pull request #2525 addressing MBS-12042.

Currently the changelog field in annotation editing form is undocumented and is most often skipped.

The purpose of this field is to summarize the content of the change in annotation history. It complements the edit note which is supposed to explain the reason and the source for the change.

If an explanatory paragraph is added above of the changelog field (just the same way it is already made with annotation and edit note fields), it seems reasonable to require it to be filled, as changelog saves a lot of time when looking at annotation's history.