copying out existing versioned-serializers code into shared/serializers/, adding into available serializers, doing proper imports and references.
cleanup from debug session that I missed in initial self-code-review.
Merge branch 'develop' of github.com:learningequality/ka-lite into save_the_django_serializers
cleaning cruft from django's serialize object
re-enabling fixture tests
OMG a merge conflict in a docstring. LOL
Added tests for VideoLog and ExerciseLog saving, including 2 that fail.

Also, minor cleanup on imports on securesync tests. They still pass.
Show valid link in alert for tabular coach reports.

Fix for #288.
Sort exercises within topics by difficulty (determined by x,y position in
sub-topic map).

Fix for #222
making this all work with ungrouped students
fixing undesired, debug-related cruft
ignore validation errors in UserLog; they can't be handled.
Merge pull request #263 from bcipolli/save_the_django_serializers

Save the django serializers
Merge pull request #331 from bcipolli/fix_two_bugs

Fix two bugs: coachreports ignore ungrouped students, students can't see their own coachreports
Added tests for creating/updating exercise logs via the API.

The updating test currently fails, due to a bug in the code to be fixed.
Removal of unnecessary code in generating link URL.
Merge pull request #330 from rtibbles/tabular-link

Enable link alert and exercise sorting on tabular coach report view
Added tests for video log saving, with wrapper for Client to do logins etc
Merge branch 'develop' of github.com:learningequality/ka-lite into fix_main_log_saving

Conflicts:
	kalite/main/tests/__init__.py
Fixes to address comments in pull request.