add changed content to email notifications+discussion

This was actually challenging when we were using the rails views, because it was hard to render cards outside of the context of a web request, but it should be really straightforward now.  Just haven't gotten back to it.  Changing from Idea to Ticket.

I suspect there will be a strong desire for diff views here as well. Either way, just a matter of rendering what you want for the mail instead of the page.

  --Gerry Gleason.....Sat Apr 21 03:41:05 +0000 2012

see also remove extra spaces in notification emails

  --Ethan McCutchen.....Sat Apr 21 19:19:10 +0000 2012