Feature/team creation notification

- Overloaded save method for Team model. An on-site notification gets sent to the currently logged in user about team creation,
- Added a task to send on-site notifications to the team captain,
- As the team captain membership gets saved later in the code, had to pass the currently logged in user's id to the team object,
- Added notification templates

This fixes #71

Thanks @statico! I'll take this into consideration.