Added trailing slashes otherwise the course_id regex sometimes eats up get parameters.

LMS-2738
BLD-725: ChoiceGroup i18n.
Fix exception on Internet Explorer when adding first transcript language

Internet Explorer throws an "Invalid argument" exception when uses an empty string as the parameter in ```namedItem``` method.
Change empty string into null value can maintain browser consistency.
Do not persist anonymous ids when exporting for all students of a course.

For large courses this causes export to take a long time and to time out.

LMS-2747
DOC-362, another set of students who don't get email
BLD-1103: Fix ChoiceTextResponse.
Merge pull request #3902 from edx/anton/i18n-choice-group

ChoiceGroup  i18n.
Merge pull request #3879 from edx/usman/lms2747-anonymous-ids-collection

Do not persist anonymous ids when exporting for all students of a course.
Merge pull request #3833 from edx/usman/lms2738-verify-student-urls

Added trailing slashes to verify_student app urls.
JavascriptResponse i18n. [BLD-737]
Merge pull request #3918 from edx/jmclaus/i18n-javascript-response

JavascriptResponse i18n.
Merge pull request #3916 from edx/anton/fix-choice-text-response

Fix ChoiceTextResponse.
Merge pull request #3892 from louyihua/ie-fix

Fix exception on Internet Explorer when adding first transcript language
Merge pull request #3909 from edx/ahodges/documentation/DOC362

DOC-362, another set of students who don't get email
Add span tag.