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
@dan-f make sure there is a test in test_item for the fact that republish is ignored for DIRECT_ONLY_CATEGORIES. See the existing test_republish test case for an example.