Add link to email that cfbot got patch from

[JelteF]

There's a little letter icon on the cfbot website next to each patch, that links back to the email thread (the link with the "envelope" symbol): http://cfbot.cputube.org/index.html

We should add that link somewhere on the commitfest app too. It should at least be on the patch detail page. Maybe we can fit one on the commitfest overview page too (we have limited space there though and I'm not sure this fits the usefulness bar).

[JelteF]

To make this work, the CFBot needs to be changed slightly to send this link.