E-mail address link in Notifications is now a mailto:

Notifications that show the author email will now be mailto links to
that email.

Fixes CNVS-15430

Test Plan:

- Enable the Show email in notifications account preference
- Generate the folloowing notifications
	- Announcement Reply
		- Enable the notification preference
		- Create an Announcement
		- Reply to it
		- Check /users/[user_id]/messages
	- Conversation Message
		- Create a Conversation
		- Check /users/[user_id]/messages
	- New Discussion Entry
		- Create a discussion
		- Add a comment to it
		- Check /users/[user_id]/messages
	- Submission Comment
		- Not really sure??
	- Submission Comment for Teacher
		- Not really sure??

Change-Id: Iafab62d7492f749a8021bdf57d43c93315285e2f
Reviewed-on: https://gerrit.instructure.com/41111
Reviewed-by: Joel Hough <joel@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Brad Horrocks <bhorrocks@instructure.com>