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
Why use containerPage.model.get('staff_lock_from')) instead of keepImplicitStaffOnly? I'm confused about why keepImplicitStaffOnly is necessary.