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
can you please avoid calling get_real_user twice as it does database lookup.
may be you can do in line 349:
```
+        try:
+            real_user_object = self.runtime.get_real_user(self.runtime.anonymous_student_id)
+            self.can_retrieve_user_object = True
              self.username = real_user_object.user_name
              self.user_email = real_user_object.email
       except:
              self.username = None
etc.
```