Reduce noise of event email notices

 - Suppress notices if the sanitizer sees no problematic HTML in the
   message.
 - If the sanitizer does see problematic HTML, present a simplified
   semantic explanation of each potential problem in the HTML.

Ideally, this will make it easier to notice exactly what might be a
problem.
Include cheerio in package.json
Add wait to create-hoa test
Adjust test split as an attempt for consistency

More from issue #267
Merge pull request #284 from drewww/event-edit-notices

Event edit notices