Add ability to set staff lock from course outline

STUD-1851. @cahrens please review.

Sandbox available at http://studio.benmcmorran.m.sandbox.edx.org/course/edX/Open_DemoX/edx_demo_course
I believe this dialog is only ever shown for chapters, sequentials, and verticals. So this check can be removed.

See isEditableOnCourseOutline