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
@mhoeber There's been some back and forth on this. Currently, clearing the hide option from a section or subsection that contains units with unpublished changes will not publish the changes, and those units will appear in a draft state. Clearing the hide option for individual units will behave like it does on the unit page, publishing any unpublished changes.