Studio/LMS: Text Justification Styling Classes/Presets for Table-based Displays (Units/Announcements)

This adds in standard text-justification class names authors can use within table cells. A request made by Olga and @allpwrfulroot. Following classes should be added to &lt;th&gt; or &lt;td&gt; element:

* cont-justified-left - left justifies content in cell
* cont-justified-right - right justifies content in cell
* cont-justified-center - center justifies content in cell

The addition of these properties was not a clean process and the rules are repeated in several places (along with dependencies on different app Sass variables) - a much larger clean up needs to happen at some points but is out of scope for this small course support request.