DONE
1. Updated get_matched_subscription_patterns() - https://codereview.appspot.com/10950045/
2. Updated user subscription tests - https://codereview.appspot.com/11215045/
3. Described on EP mail notification implementation
4. Worked on the format (diff and visualization) of meta revisions diff.
5. Checked how subscribed_pages were assembled in moin19 and left a comment about that on cr
TODO
1. Write a meta diff function
2. Create notification templates