EDX-246: Add feature for entrance/exit survey
EDX-246: Add survey section in Beta Instructor Dashboard
EDX-439: Fix encode error when downloading survey csv
EDX-446: Fix survey items of csv file

Fix a bug for the case that one survey has different survey items
from others in a course.
EDX-510: Remove 'Gender', 'Year of Birth' and 'Level of Education' from survey csv.
EDX-687: Modify course_id for OpaqueKeys
Merge pull request #171 from yokose-ks/EDX-246

EDX-246: Add feature for entrance/exit survey