Orangered emails: don't escape entities

@umbrae and @powerlanguage both noticed that certain characters (angle
brackets, quotes) were being html-escaped in the emails.  Since the emails are
currently only plaintext, this looked weird and required a mental translation
back to understand what the prior markdown looked like.

This should continue to be safe as long as we're only sending plaintext emails.

r2/r2/templates/messagenotificationemail.email

@@ -26,6 +26,6 @@
 
 ${_("You've received a new message!")}
 
-${thing.comment.body}
+${unsafe(thing.comment.body)}
 
 ${_("View on the web")}: ${thing.permalink}