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
What's wrong with the current display? They will only appear if the content was locked and you uncheck the box, because the visibility of the `.tip-warning` class is tied to the checked state of the checkbox.