Add MathJax config option allign left

Previously, MathJax was rendering display style math allign: "center",
while KaTeX rendered allign: "left". This has been addressed.

h/static/scripts/directives/markdown.coffee

@@ -8,6 +8,7 @@ loadMathJax = ->
         # MathJax configuration overides.
         MathJax.Hub.Config({
           showMathMenu: false
+          displayAlign: "left"
         })
     }