Integrate UI text strings from doc

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Switch live content warning based on unpublished changes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Change "Unpublished (Staff only)" to "Visible to Staff Only"
Merge pull request #4628 from edx/benmcmorran/doc-text-update

Integrate UI text strings from doc