Added HTML receipts (bug 890046)

This is a non-work contribution... it seemed fun so I threw this together Sunday morning over tea.

What's left to do:
[ ] Update text based email for the same data as in the HTML.
[ ] Add tests, at least for the context passed to the templates.

I'm using old school all caps HTML to suggest this is HTML in an email, which is stuck in the 90's due to email clients.

The result looks like this:
![screen shot 2013-07-14 at 1 46 02 pm](https://f.cloud.github.com/assets/1106/794902/d34d266c-ecc6-11e2-95e8-f6b653683beb.png)