Add ADDL_INSTALLED_APPS to studio for parity with lms
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
Increase async script timeout in lettuce tests
Increase the default timeout for waiting in lettuce tests
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
Merge pull request #3882 from edx/ammar/test-youtube-availibility

Check YouTube Availability for Video Tests
Merge pull request #3927 from edx/ahodges/documentation/DOC438

corrected a typo; tried to clarify a different sentence
Merge pull request #3896 from edx/will/install-ease-and-requirements

Install EASE and requirements
Move to OpaqueKey implementations from the external library

[LMS-2757]