STUD-1856
Display "IS VISIBLE TO" when released and published
Reword staff lock prompt and notifications
Change "View Published Version" to "View Live Version"
Change "Unit Tree Location" to "Unit Location in Course"
Switch live content warning based on unpublished changes
Reword discard changes confirmation prompt
Reword unit location tip
Add "Edit the name" popup text for sections and subsections
Fix popup text for section and subsection titles
Add popup text for new section, subsection, and unit buttons
Reword popup for View Live button and add tests
Reword notification when removing staff lock
Update MessageView when has_changes changed
Change "Published" to "Published (not yet released)"
Change "Unpublished (Staff only)" to "Visible to Staff Only"
This commit implements STUD-1490, allowing creation of components
on the container page. It also enables the delete and duplicate
buttons now that new content can be created that would benefit.
Note that it also creates shared functionality for adding components,
and refactors the unit page to use it too.
