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

@statico: Thanks for pointing this out. I followed your suggestion and changed not only this specific case but also the team invitation part.