Allow moderators to forcibly change the username of other users. This is
so mods can change abusive or invalid usernames.
* A mod can only change the username of Builder-level users and below.
* The user can't change their own name again until one week has passed.
* A modaction is logged when a mod changes a user's name.
* A dmail is sent to the user notifying them of the change.
* The dmail does not send the user an email notification. This is so we
don't spam users if their name is changed after they're banned, or if
they haven't visited the site in a long time.
The rename button is on the user's profile page, and when you hover over
the user's name and open the "..." menu.
Remove all infrastructure around approving or rejecting user name
changes. Name changes haven't been moderated for several years.
* Remove status, approver_id, change_reason, and rejection_reason fields.
* Remove approve and reject controller actions.
Fineprint text was variously styled with `.info`, `.tn`, `.hint`, or
`.cost-footnote` css classes. Standardize on `.fineprint` instead. Use
`.hint` only for form hints and `.tn` only for <tn> tags in translation
notes.
Incidentally changes the font size of form hints to 0.8em (was 0.7em)
and the color of fineprint to #888 (was #AAA or #666).
