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
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