Add ADDL_INSTALLED_APPS to studio for parity with lms
Added trailing slashes otherwise the course_id regex sometimes eats up get parameters.

LMS-2738
BLD-725: ChoiceGroup i18n.
Extract opaque_keys into a separate library

[LMS-2571]
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
Moved hardcoded defaults into settings
Fixes some stuff in metrics tab
  Fixes some 500s after opaque-keys
  Adds a test which would have caught the 500s
  Fixes Transifex problem on the string % of students
Build 'window.location.origin' for Internet Explorer

As TinyMCE's CodeMirror plug-in uses 'window.location.origin' which is not supported by Internet Explorer, the HTML or raw code editor does not work under Internet Explorer.
We need to create one in order to make these vendor codes work under Internet Explorer.
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.
Increase async script timeout in lettuce tests
Merge pull request #3892 from louyihua/ie-fix

Fix exception on Internet Explorer when adding first transcript language
No longer chunk queries when sending out bulk email (LMS-2718)

refactor _generate_items_for_subtask not to chunk queries

use django's iterator methor for querysets

remove bulk email query settings

use read_replica if available, since this is read-only

update changelog