forums: fix assign_default_role to use the correct constant.
Fix the CoursePagesTest
trigger change event for file field while uploading pdf
STUD-1775
implement forums endpoint for searching users
Merge pull request #4041 from edx/jsa/forums-search-users

implement forums endpoint for searching users.
Merge pull request #4089 from edx/zoldak/courses-test

Fix the CoursePagesTest
Merge pull request #4054 from edx/zub/bugfix/std1775-uploadpdfbutton

trigger change event for file field while uploading pdf
Revise course mode choose page.

LMS-2796
Merge pull request #4108 from edx/diana/update-choose-form

Revise course mode choose page.
bugfix: avoid side-effects when overriding User.default_retrieve_params
Merge pull request #4118 from edx/jsa/bugfix-cc-user

bugfix: avoid side-effects when overriding User.default_retrieve_params
fixup! Fix i18n translation issues
Youtube Video Quality Button Tests