Add survey links to instructor profile

[elichad]

Fixes #2016 .

I used the instructor_pre field, but we could also use the reports_link function to generate the URL on the fly. I chose the former as some events don't seem to have survey links at all (especially older ones) and some point to surveymonkey links. Any thoughts on this?

Side question though: how/when is instructor_pre actually set? I assumed it's automatic if we can generate the links automatically, but I can't find it in the code.

[pbanaszkiewicz]

@elichad According to documentation, instructors_pre is not used, but I can see it appears on EventForm, probably editable by the user. @maneesha can you confirm that?

[elichad]

Confirmed in a meeting with @maneesha that we are actively using instructors_pre as part of the Event form. I've updated the documentation accordingly.