[STUD-256] Seems like on chrome when cancel is hit in the file chooser, the 'change...

Fix broken lettuce tests

Feature/dhm/timeconv

Update lettuce test for problems with new css for show and hide answers.

Seems like on chrome when cancel is hit in the file chooser, the 'changed' event is fired and startUpload() was being called. We need to check to see if the upload file is blank and - if so - just return immediately out of the function

A number of important accessibility changes

Reviewed by @brianhw https://rbcommons.com/s/edx/r/17/

lms - adds back in missing/previously added .sr screen reader-focused styling and references in place of the .visuallyhidden application

adds in status for overall problem status indicator and replicates needed correctness django logic to show individual choice status

courseware active location, suppress browser form validation, and progress graph accessibilit changes