MathJax support

Ticket [#LATEX-66] and [#LATEX-67] could be solved based on MathJax, which displays formula very nicely and supports references to equations as well as a wide range of LaTeX environments.

All that needs to be done to use MathJax with XWiki is to copy the distribution to resources/MathJax and to append

<script type="text/x-mathjax-config">
  MathJax.Hub.Config({
    displayAlign: "left",
    displayIndent: "2em",
    TeX: { equationNumbers: { autoNumber: "AMS" } }
  });
</script>
<script type="text/javascript" async
  src="/xwiki/resources/MathJax/MathJax.js?config=TeX-AMS_CHTML">
</script>

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