Documented general.py

refs #16299
Added note for what USER_PERMS are for.

refs #16299
Added some documentation for Form classes.

It may seem a bit redundant, but it will be useful when we auto-generate
docs and have something to describe the classes.

refs #16299
Updated documentation on models.

refs #16299
Added more precise documentation for utils.

refs #16299
Added some documentation for manage.

refs #16299
Added comments to install_course.js

refs #16299
Added some comments for migrate.js

This file should be cleaned up, it looks like a tornado hit it.

refs #16299
Added comments for report.js

refs #16299
Added comments for update_models.js

refs #16299
Merge branch 'bug/16299' into develop
controllers: Fixed type on current_app.

refs #16215
install_course: Added missing vars/funcs.

Was missing install_course_to_site from util.py and the filtered courses list,
which was probably lost somewhere in some merge conflicts.

refs #16215
celery: use the app_context

refs #16215