exam_feedback endpoint modeled after interactive_exercise (#1449)

Not tested yet, need to merge first.
Merge branch 'master' of github.com:Stanford-Online/class2go into sef-1449-grader

Conflicts:
	main/urls.py
Pass all data- elements as params for interactive exercises (#1620)
store invideo exam results back, wrong fmt (#1449)

The format of the json_data and json_score_data still aren't correct
Merge branch 'master' of github.com:Stanford-Online/class2go into sef-1449-grader
in video exercises: scoring feedback, hide button (#1449)
Merge branch 'master' of github.com:Stanford-Online/class2go into sef-1449-grader
fixes #1667 auto sets 'invideo' flag for exam with <video> xml
Assessment Summary report which replaces Problem set summary report
(#1595)

As it turns out, this was quite simple as it is a report of a single
assessment with same format as the Combined Summary Assessments
report.

Also, includes some final cleanup of the old problem set reports that
are no longer required.
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working
fixes #1666 tracks slug changes on edit page and adjusts endpoint
Deploy recipe: prune branches (#1664)

while I was in here added app name to the commands so we can see
in the chef log.  Helpful for debugging.
Add app name to collectstatic cmd for logging (#1664)
declutter chef output by saving away collectstatic (#1677)
Return file download links to video display page
Refactor simplifying frequent template variables

* Use {% with %} to cache frequently-referenced variables in item list
  view templates
* Also change templates/files/[draft|ready]/file_list_item.html
  references to file.url back to file.file.url
  (closes #1585)
Merge pull request #1668 from Stanford-Online/jbau-xml-video

fixes #1667 auto sets 'invideo' flag for exam with <video> xml
Merge pull request #1675 from Stanford-Online/jbau-exam-save-fix

fixes #1666 tracks slug changes on edit page and adjusts endpoint
Merge pull request #1679 from Stanford-Online/jrbl-1563-listing-files-on-videos-master

Return file download links to video display page
Merge pull request #1681 from Stanford-Online/jrbl-1585-file-file-url-master

Refactor simplifying frequent template variables