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

You don't have to change anything here, but in the future you might want to consider using the `{% blocktrans %}` tag instead: https://docs.djangoproject.com/en/1.7/topics/i18n/translation/#blocktrans-template-tag

If the sentence is later translated, the translation might be to a language whose grammar is different, and the link might appear in the middle or beginning of the sentence instead of the end.