#2282 added review tab for page versions

[symmetrically]

[saracarl]

This PR implements more or less what an academic transcriber sketched out in #2282.

There are some implementation problems, namely no line breaks and no mark-up, which means this isn't very useful:

But there's a much bigger problem, which is "what's the purpose of this tab?"

Was the intention of this to be able to load the page source at a given revision and compare it against the facsimile? To what point? I feel if you're are going to review, you must be able to edit. But do we really want any transcriber to be able to set a page back to an earlier version and save it? I'm not sure we do. (This becomes effectively "revert", #2744)

@benwbrum to review.

[benwbrum]

Replaced by #4289