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
Is this conditional necessary? Don't we only show this dialog for things that are editable (as returned by          isEditableOnCourseOutline)?