Updates based on merge with master.
First pass at locking.
First bok choy test for visible_to_staff_only.
First cut at staff lock UI
Show the correct block color for all states
Fix merge issue.
Implement first set of staff only tests
Fix publishing unit tests
BDD text.
Fix remove lock test to confirm first
Bok choy tests for staff locking from Studio unit page.
Small BDD wording change.
Address code review comments
Make the container messages refresh dynamically
More bok choy tests around locking interaction and display of release date.
style adjustments for staff only sidebar on unit page; removed unused styles for unit location tree
Improve UX on 'Hide from Students' button

 - uses a font awesome icon instead of a check box
 - adds ARIA support for screen readers
checkbox for hide from students on unit page
Adds more comprehensive bokchoy testing for publishing changes
Adds minimal testing of last published and saved dates