This avoids duplicate calls to Check.get_grace_start() in several places.

when 10 or less remaining.

Based on this change:
166115ebfb

I wanted to check the cron cheatsheet and got annoyed because it opened on the same tab, so I had to go back and open the window/modal to edit the cron period, and open the cheatsheet again, but this time on a new tab, so I could build my cron expression side-by-side.

services like https://ifttt.com/maker_webhooks which require a
specific content type, like application/json.

Apply the user's chosen sort order in emails also.