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.
Why is this customizable? I'm not sure that we'd want or expect users to
change this.

It seems like this is used as a flag, whether or not to append the
`anon_user_id` to the query string. Assuming that's the expected use
case (and instructors don't actually want to customize this), I'd like
to see this switched to a Boolean field, `should_append_anon_user_id`. 
This could be toggled with radio buttons or some such.

Given that the rest of the URL is hard-coded, I'm not sure what we get
from customizing this one query param. Of course, let me know if I'm
oblivious to some use case.

cc @jinpa