Capa and HTML xmodules: Text Justification Styling Classes Table-based Displays

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.

Also, my editor has stripped out whitespace from these files (a good thing, methinks).