Add link to issue to noficication mails (BB-7956)

When a comment is placed on an issue, the notification mail body looks like this:

— you can reply above this line —

Issue 797: Make flexible setup to retrieve all commits for changelog
/marcinkuzminski/rhodecode/issue/797/make-flexible-setup-to-retrieve-all

Marcin Kuzminski:

configurable option is now merged to beta.

Changes:
status: new -> resolved

–

This is an issue notification from bitbucket.org. You are receiving

this either because you are the owner of the issue, or you are
following the issue.
Meaning there is no http link to the issue itself, which is kind of bad to be honest.

Solution: Add a link to the issue in the mail body so users can easily browse to the updated issue.