Issue #2162409 by jibran, Wim Leers, nod_: Split up contextual.js.

core/modules/contextual/contextual.module

core/modules/contextual/js/contextual.js

core/modules/contextual/js/models/StateModel.js

core/modules/contextual/js/views/AuralView.js

core/modules/contextual/js/views/KeyboardView.js

core/modules/contextual/js/views/RegionView.js

core/modules/contextual/js/views/VisualView.js