No links in notification e-mails (BB-7894)

I never trust "reply to this e-mail to reply to the issue" systems (no way to preview how it's going to look) so I find BitBucket's issue tracking annoying because I have to manually pull the issue out of my Firefox history every time I want to respond.

(Thank goodness 99% of the bugs I follow are on GitHub and thank goodness for the AwesomeBar. If I were on Chrome, it'd take forever and only the non-local results would be relevant.)