Changed str->unicode in common/djangoapps/utils/.

LMS-2436
Some more str->unicode fixes in instructor and courseware apps.

LMS-2429
Revert to older version of TinyMCE.

We had trouble with Cloudfront/hashed files and need more time
to investigate.
This reverts commit e8f53ac9dc6d8a1d9928787635c7c5f7e409a9ec.
Merge pull request #3067 from edx/christina/revert_tinymce

Revert to older version of TinyMCE.
Merge pull request #3070 from edx/adam/middleware

wiki middleware fix (LMS-2461)
Concept added to Studio advanced components
Update testing.md file.

How to run Python tests for stub servers.
Merge branch 'release'
Fix failing tender.
Merge pull request #3092 from edx/valera/fix_tender

Fix failing tender.
Update doc string for YouTube stub server.

Included information on how to launch the server
on its own.
EOF
Add an option to prevent multiple logins of the same user.
Merge pull request #2793 from edx/dcs/mat-17

Add an option to prevent multiple logins of the same user.
Fix broken test due to refactoring.
LMS-1287: Added section for batch add of beta testers
Merge pull request #3071 from edx/ahodges/documentation/bulkbeta

LMS-1287: Added section for batch add of beta testers
Support emitting analytical events from xblocks running in the LMS

XBlocks can and should use the "publish" method provided by the runtime to emit analytical events. In theory we could now start replacing calls to track_function with calls to publish, however, that migration is not handled by this change.

Fixes: AN-789
Reduce false cache misses when evaluating prerequisites
Merge pull request #3090 from edx/valera/update_youtube_stub_server_doc

Update doc string for YouTube stub server.
Make YouTube mocked server serve YouTube API

1.) Making YouTube mock server serve YouTube API.
2.) Adding ability to block YouTube API from YouTube mock server.
3.) Adding acceptance tests that check YouTube mock server for availability of YouTube API, and for it's ability to block YouTube API.

Part of BLD-939.