[bug 1079376] Add error-email -> response admin view

This adds an admin view that lets me add feedback that errored out when
it was posting to Input by relevant part of the copy-and-pasting the
error email. This is a stopgap until Input has 5 9s.
Merge pull request #359 from willkg/1079376-response-page

[bug 1079376] Add error-email -> response admin view