TE-447

STUD-2058

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Switch live content warning based on unpublished changes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Change "Unpublished (Staff only)" to "Visible to Staff Only"

STUD-1967

STUD-1873

STUD-1860

STUD-1707

STUD-1754

STUD-1658

STUD-1312

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.