Make some Herald errors more spider-resistant

Summary:
Fixes T9328. There's no way to hit these error states by clicking things in the UI that I could find, but if you mash stuff into your URL bar or "Inspect Element..." and then edit the form to be full of garbage you can hit them.

Make them a little more informative and don't send them to the log, since these are pretty much just fancy 404s.

Test Plan: Bashed my fist on the URL bar to hit all these messages.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9328

Differential Revision: https://secure.phabricator.com/D14164