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
Nit: lines 478-483 could be a helper method (passing in the item which should have its lock toggled), and the code shared with the test before and the test after.