Multiple-choice features

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)
Merge pull request #3302 from edx/renzo/analytics-improvements

Add more granular pageview tracking, update Segment.io snippet
Merge pull request #1499 from edx/nick/shuffle-question

Shuffle feature for multiple choice questions
Serve video HTML5 sources locally for acceptance tests
Update Running Acceptance Tests Bok_Choy
Update testing documentation
Merge pull request #3331 from edx/zoldak/serve-test-videos-locally

Serve video HTML5 sources locally for acceptance tests
Fix duplicate save and cancel buttons in Studio

STUD-1531

Also add support for refreshing the modal on custom save
Updated ORA2 to release-2014-04-15
Merge pull request #3339 from edx/andya/fix-duplicate-buttons

Fix duplicate save and cancel buttons showing when editing xblocks
Fix duplicate save and cancel buttons in Studio

STUD-1531

Also add support for refreshing the modal on custom save
Merge pull request #3361 from edx/andya/rc-fix-duplicate-buttons

Fix duplicate save and cancel buttons in Studio
Merge pull request #3359 from edx/will/ora2-release-2014-04-15

Updated ORA2 to release-2014-04-15
Fix batch enrollment box email sending
Documentation for HTML editor upgrade

STUD-1428
Merge pull request #3022 from edx/markhoeber/documentation/STUD-1428

First Draft - Documentation for HTML Editor Changes
Merge pull request #3362 from edx/sarina/fix_batch_enrollment_emails

Fix batch enrollment box email sending
Release notes 4-15-14
DOC-253, adds View in Studio button to LMS
Merge pull request #3351 from edx/ahodges/documentation/DOC253

Ahodges/documentation/doc253