Users may want to start anew when answering a question. This commit decouples reset from randomization while still preserving backward compatibility. Users can clear their input.
Instructors can set course-wide and problem-specific settings for reset button display.

LMS-11194

STUD-1726

STUD-1754

STUD-302, STUD-303

STUD-1629

STUD-1514

Features by Jeff Ericson and Nick Parlante squashed
down to one commit.

-shuffle of choices within a choicegroup (Nick)
-answer-pool subsetting within a choicegroup (Jeff)
-masking of choice names within a choicegroup, (Nick)
 used by shuffle and answer-pool
-targeted-feedback within a multiplechoiceresponse (Jeff)
-delay-between-submissions capa feature (Jeff)

http://bgrins.github.io/codemirror-accessible/)
LMS-1802

This bug affected unpublishing content (and would trigger an error
message in studio). The fix was to uncouple the rendering of the studio_view
of an xblock with the student_view, so that content that wasn't in
draft mode already wouldn't be modified by early rendering of the
studio_view.

[STUD-1316]

Part of STUD-847.

BLD-426

Make tests conform to new import UI

Also change test to not expect text_customization

Cleaned up files with muliline imports

Cleaned up files that do not use these imports

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