Fix bug affecting video transcripts in XMLModulesStore courses
Reformatted tables, copy edited, and proofread.
Merge pull request #3722 from edx/ahodges/documentation/DOC156

Ahodges/documentation/doc156
Add sjson and srt to type map.
Merge pull request #3648 from edx/oleg/fix-download-transcript

Add mime-type for srt and sjson when importing course.
Merge pull request #3725 from carsongee/cg/transcript_xmlmodulestore_fix

Fix bug affecting video transcripts in XMLModulesStore courses
Merge remote-tracking branch 'edx/master' into opaque-keys-merge-master

Conflicts:
	common/lib/xmodule/xmodule/video_module/video_handlers.py
Fix merge conflicts
Fix instructor csv download