Refactor notifications.email into a module

Review Request #8829 — Created March 20, 2017 and submitted — Latest diff uploaded

Information

Review Board
release-3.0.x
72646df...

Reviewers

email.py was getting long and it is past due that it was split up.
This patch is in preparation for another change that will add more
e-mail-specific code.

Ran unit tests.