username and email request for lti module

Necessary for MIT course starting early October. Please merge as soon as possible to facilitate feature testing.

added username and email functionality, so that username and email can be passed to the lti third party app
better is do it like:
```
        self.user_email = ""
        if self.runtime.get_real_user is not None:
            self.user_email = self.runtime.get_real_user(self.runtime.anonymous_student_id).email
```
As get_real_user will return None if user is not found, and you do not need to catch all types of exceptions.