cleanup of unit, container, and xblock sass; added modules and layout sass; publishing states and actions on new unit

STUD-1754

STUD-1312

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

STUD-1306

styling for recursive xblock rendering structure to be used in the container page, pulling from general xblock styles in a separate file.

updated container header styling and exposed sidebar back to its location. includes some javascript to render tooltips on overflowed text headers

STUD-1186

* add HTML for links
* hide links when they are not focused
* when focused, show link (as recommended)
* move accessibility tools to common

LMS-1311

Also includes RequireJS changes.

Fixes bugs:
STUD-755, STUD-152, STUD-700, STUD-699

Studio: updates older extend references and solves Sass warnings/dupe display of accessibility-based text

Bourbon's box-shadow mixin has been deprecated, and they recommend to use the
official spec.

The official border-radius mixins were deprecated and removed in Bourbon 3.0.
https://github.com/thoughtbot/bourbon/pull/95

(cherry picked from commit 832da3ad)

removed symbolset, replaced with fontawesome for gradable status; added transform-origin for saving notification animation to remove wobble

removed symbolset, replaced with fontawesome throughout for new buttons; updated old code for new button at bottom of grading to also use the FA style

typography, SASS, imports

typography, SASS import, mixins/extends