A change cannot be updated once created, so its screenshots cannot be set over REST

The two properties that could not be written after a change or a release note was created now can: the screenshots of a change, whose names must already be attachments of a page the creation itself allocates, and the released and date of a release note, which are only known on the day the version ships.

Added in 2.8:

• GET and PUT on one release note, at /wikis/<wiki>/releasenotes/<product>/<version>.
• GET and PUT on one change, at /wikis/<wiki>/releasenotes/<product>/<version>/changes/<entry>. The entry page name is now answered by ChangeRepresentation as entry, so a client never has to parse it out of a page reference.
• ChangeManager#updateChange and ReleaseNoteManager#updateReleaseNote on the Java API, both also exposed on the script service.
• ReleaseNotesNotFoundException, mapped to a 404 by the exception mapper.

This answers the open question on this issue: illustrating a change stays a three-call flow and needs no attachment endpoint of ours. Create the change, attach the image through the wiki's generic attachment API against the page the response carries in reference, then PUT the change with the names added.

Two things worth knowing before using it:

• A PUT replaces, it does not merge. A property the request leaves out is emptied, so send back the change the creation answered with the screenshot names added, rather than a partial body. A change left with no importance is displayed by no release note.
• The product and the version are never replaced by either endpoint: they locate the page, so changing them would be a move of that page rather than an update of its properties. The content, the title and the template of a release note are left alone too, since an administrator is free to have edited that content.

before.png is what a client could produce before, after.png the same change after one PUT.