adding django admin command to change enrollment
fixing example
grammar
JavaScript extentions doc update

doc-255
User doesn't exist in verify student banner toggle off view
LMS-2510
Merge pull request #3410 from mlkwaqas/waqas/lms2510-banner-toggle-off

User doesn't exist in verify student banner toggle off view
Merge pull request #3267 from edx/markhoeber/documentation/doc-255

JavaScript update in developer documentation
Merge pull request #3396 from edx/jarv/change_enrollment_cmd

adding django admin command to change enrollment
Add several acceptance tests for start-time and end-time.
Fix tests.
Addressing reviewer's comments.
Fixing test.
Fixing test.
Fixing test.