BLD-1911: Publish units from course outline.
Studio: adding styling for batch publishing modal UI
* abstracting simple vs. complex outline UI styling
* specific modal UI styling for publishing confirmation
UX-676

Conflicts:
	cms/static/sass/elements/_modal-window.scss
	cms/templates/ux/reference/modal_bulkpublish-section.html
	cms/templates/ux/reference/modal_bulkpublish-subsection.html
	cms/templates/ux/reference/modal_bulkpublish-unit.html
Update UI.