Fix bug affecting video transcripts in XMLModulesStore courses
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
Correcting "make html" errors
Merge pull request #3737 from edx/ahodges/documentation/fixup

Correcting "make html" errors
i18n: Make translation works for video editor tabs

Now the display_name & help strings in video editor tabs can be extracted and translated.