Support staff locking on the unit page

STUD-1873
Merge pull request #4412 from edx/christina/staff-locking

Support staff locking on unit page
Studio: adding static course outline reference template (w/ initial working HTML)
Studio: revising static course outline reference template

* static markup for all section states in outline UI
* static markup for all subsection states in outline UI
* static markup for all unit states in outline UI
Studio: styling revamped course outline-related UI

* adding in outline-related color values
* styling for publishing states
* light styling abstraction for specific outline and unit/container contexts
* revising add item to outline button styles
* adding a few bells and whistles (hover states and error pulsing)
Studio: revising draft/unscheduled item status in outline UI
Studio: syncing up page-level action button classes/styles
Studio: revising in-context title editing markup out outline UI
Studio: cleaning up Sass partial formatting
addressing PR feedback