Notification app for, in first hand, e-mail notifications

[frjo]

• Create a notification app that holds templates and core functionality for sending notifications.
• Move each notification from EmailAdapter to a notifications.py for each app, like fund, project etc.
• Notification function are named consistently in the form notify_<model>_<event>(), e.g. notify_submission_new(). A functions sends all notification for that event.
• Rename funds/notificaitons.py to funds/notifications.py