Studio: updating Sass ui-disabled placholder syntax and creating utility is-disabled class

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
Add javascript backup if pointer-event is not supported by browser

(STUD-1498)
Merge pull request #3101 from edx/talbs/ui-disabled

UI: Disabled Utility Classes