Notifications: move all notificatications related emails to notifcations app.
Increment djmail version to 0.6
Add helper import on __init__ of mdrender.
History: improvements on history app

- Handle deleted objects.
- Add project to freezers.
- Make values implementation optional.
- Split choices to separated module.
- Add own mixin.
Minor fix on project creation.
Notification: new notification application.
Notifications & History: modify all related models and resources for work with new api.
Add additional factories for tests.
History: add tests.
Notifications: add test for notifications app.
Add some utils function for text management for query.
Remove old notification mixin.
Cosmetic fixes on references services and user form.