Fixed broken link to install_course.

We also now use url_for, since it is more dynamic and doesn't
require us to change the target url on the template if we change
the endpoint. (It refers to a function for a url, rather than it being
hardcoded)

refs #16251
Merge branch 'bug/16251' into develop
Added option to create default user.

refs #16239
Fixed comment.

refs #16239
Merge branch 'bug/16239' into develop
Changed return format to JSON in <category>/update

Now we can return more information other than a simple message.

refs #16245
Update now modifies select field text if changed.

refs #16245
Fixed display text.

refs #16245
Merge branch 'bug/16245' into develop
Switched to JSON for return format.

refs #16287
Now accessing returned data via JSON.

refs #16287
Merge branch 'enhancement/16287' 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
celery: fixed out of context issue

refs #16215