Studio: revising .fake-link utility class to use Sass placeholder and syncing commenting style
LMS: updating Sass ui-disabled placholder syntax and creating utility is-disabled class
Studio: adding in basic action Sass placeholder for use in enabling/disabling UI
Studio: applying action Sass placeholder to publish/create-draft Unit view actions
STUD-1497
This is the changes for STUD-1244, which introduces the ability for Studio to display
arbitrarily nested xblocks. In this change, a new container page is introduced which can
display nested xblocks. In particular, the xblock type of 'vertical' is special cased
to be shown inline as a collapsible section. The unit page is mostly unchanged, except
that container xblock's are shown as a link to their container page, rather than being
shown inline.
