(WIP) Publish units from course outline. 

**Tickets:** [STUD-1911](https://openedx.atlassian.net/browse/STUD-1911), [STUD-1932](https://openedx.atlassian.net/browse/STUD-1932)

**Acceptance criteria:**
* Selecting the Publish option from the course outline should bring up a pop-up confirming the publication of all unpublished changes for the unit, with options to publish or cancel publishing. 
* All course content in that unit should be immediately be set to “Public” and be visible to students if the release date is in the past. 

Sandbox: http://tymofij.m.sandbox.edx.org/
This variable name no longer makes sense (you are checking has_changes regardless of whether or not it is a unit). Also, you will have to do performance profiling of the course outline page (and verify the number of mongo queries). Previously, has_changes was a very expensive operation, and we could not afford to call it in general for all xblocks on the course outline. With the recent reduction in mongo calls that @benmcmorran did, we think this is no longer an issue, but it should be verified.