V1 for notification system complete

- Users who subscribe and confirm will:
  - receive 1 email for EACH property that
    - they subscribed to
    - has seen activity in the last week

- TODOs
  - Style + Content for everything
  - Wrapping up all properties into one Email by NotificationSubscription.email
  - Keeping track of activities in the NotificationSubscription
    - If a User subscribes on Friday, and email goes out Sunday.. he/she will see
      5 days of stale activity
    - Will allow to display actuall activity in the emails: