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
How about a test with a chapter that has 2 sequentials -- one that is staff only, and one that is not. Then the visibility state of the chapter should not be staff_only.

Right now, it doesn't seem like many variations are covered in the tests. Or perhaps those tests already exist, and I'm just not seeing them in the diff?