Add ADDL_INSTALLED_APPS to studio for parity with lms
Extract opaque_keys into a separate library

[LMS-2571]
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.
Increase async script timeout in lettuce tests
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
Increase the default timeout for waiting in lettuce tests
Merge pull request #3893 from louyihua/tinymce-ie-fix

Make TinyMCE's HTML source code editor work under Internet Explorer
Merge pull request #3862 from cpennington/external-opaque-keys

Extract opaque_keys into a separate library
Merge pull request #3921 from edx/zoldak/increase-test-wait-for-default-timeout

Increase the default timeout for waiting in lettuce tests
Merge pull request #3920 from edx/zoldak/increase-test-async-timeout

Increase async script timeout in lettuce tests
Add EASE to edx-platform requirements
Check YouTube Availabitlity for Video Tests
Merge pull request #3871 from edx/dcadams/fix_metrics_tab_after_opaque_keys

Fixes some stuff for metrics tab
Merge pull request #3717 from mitocw/cg/studio_addl_apps

Add ADDL_INSTALLED_APPS to studio for parity with lms
Allow editing of container xblocks/xmodules

STUD-1312
Merge pull request #3905 from edx/flowerhack/change-hardcoded-defaults

Moved hardcoded defaults into settings
Merge pull request #3819 from edx/andya/edit-containers

Allow editing of container xblocks/xmodules
corrected a typo; tried to clarify a different sentence