Adding UXPL classnames to headings

cms/djangoapps/contentstore/features/component.py

cms/djangoapps/contentstore/features/problem-editor.py

cms/static/sass/_build.scss

cms/static/sass/xmodule/_headings.scss

cms/templates/ux/reference/container.html

common/lib/xmodule/xmodule/css/annotatable/display.scss

common/lib/xmodule/xmodule/js/fixtures/annotatable.html

...n/lib/xmodule/xmodule/js/fixtures/crowdsource_hinter.html

common/lib/xmodule/xmodule/js/fixtures/jsinput_problem.html

common/lib/xmodule/xmodule/js/fixtures/problem_content.html

...lib/xmodule/xmodule/js/fixtures/problem_content_1240.html

common/lib/xmodule/xmodule/js/spec/problem/edit_spec.coffee

common/lib/xmodule/xmodule/js/src/problem/edit.coffee

common/lib/xmodule/xmodule/templates/html/announcement.yaml

common/lib/xmodule/xmodule/templates/html/iframe.yaml

common/lib/xmodule/xmodule/templates/html/image_modal.yaml

common/lib/xmodule/xmodule/templates/html/latex_html.yaml

common/lib/xmodule/xmodule/templates/html/zooming_image.yaml

common/static/css/tinymce-studio-content.css

common/test/acceptance/pages/lms/library.py