Qualtrics Survey Xblock

  Author fields in Studio:
   - Display Name
   - Survey ID
   - Your University
   - Link Text
   - Parameter Name for UserID

  If Parameter Name is left blank, the anonymous student id is
  omitted from the url.

  Links to an already existing Qualtrics survey.
Much of this logic appears to be duplicated between the `studio_view`
and `student_view`. The `build_fragment` method was originally created
to centralize and share common logic between the two fragments; that's
probably the best location for this logic.

I recently did something similar for the Image Modal:
```python
def build_fragment(self,
    path_html='',
    # ...
    context=None,
):
    # ...
    html_source = self.get_resource_string(path_html)
    html_source = html_source.format(**context)

def student_view(self, context=None):
    fragment = self.build_fragment(
        path_html='view.html',
        # ...
        context={
            link_text=link_text,
            survey_id=survey_id,
            user_id_string=user_id_string,
            your_university=your_university,
        },
    )

def studio_view(self, context=None):
    fragment = self.build_fragment(
        path_html='edit.html',
        # ...
        context={
            self=self,
            source_content=source_content,
        },
    )
```