WIP Mobile/video pipeline

We have some utilities you can call via Sass extends to get this same functionality - https://github.com/edx/edx-platform/blob/master/common%2Fstatic%2Fsass%2F_mixins.scss#L342. If you're looking for more semantic/a11y-friendly ways to visually hide things, there are https://github.com/edx/edx-platform/blob/master/common%2Fstatic%2Fsass%2F_mixins.scss#L361 and https://github.com/edx/edx-platform/blob/master/common%2Fstatic%2Fsass%2F_mixins.scss#L369