History: improvements on history app

- Handle deleted objects.
- Add project to freezers.
- Make values implementation optional.
- Split choices to separated module.
- Add own mixin.
History: add tests.
Notifications: new notification application.
Notifications: move all notificatications related emails to notifcations app.
Notifications: add test for notifications app.
Notifications & History: modify all related models and resources for work with new api.
Remove old notification mixin.