Discussion forum doesn't work when mathjax is down

When mathjax is down discussion forum doesn't work
as we were using markdown.js with processor as
mathjax. Unavailability of mathjax raise error in
js which stops discussion to render. So I made
markdown independent of mathjax. Markdown now will
use mathjax when it is available otherwise ignore it.

TNL-1149

common/static/coffee/src/discussion/views/discussion_thread_profile_view.coffee

@@ -10,7 +10,8 @@ if Backbone?
       @$el.html(Mustache.render(@template, params))
       @$("span.timeago").timeago()
       element = @$(".post-body")
-      MathJax.Hub.Queue ["Typeset", MathJax.Hub, element[0]]
+      if MathJax?
+        MathJax.Hub.Queue ["Typeset", MathJax.Hub, element[0]]
       @
 
     convertMath: ->

common/static/coffee/src/discussion/views/discussion_thread_show_view.coffee

@@ -32,7 +32,8 @@ if Backbone?
     convertMath: ->
       element = @$(".post-body")
       element.html DiscussionUtil.postMathJaxProcessor DiscussionUtil.markdownWithHighlight element.text()
-      MathJax.Hub.Queue ["Typeset", MathJax.Hub, element[0]]
+      if MathJax?
+        MathJax.Hub.Queue ["Typeset", MathJax.Hub, element[0]]
 
     edit: (event) ->
       @trigger "thread:edit", event

common/static/coffee/src/discussion/views/response_comment_show_view.coffee

@@ -33,7 +33,8 @@ if Backbone?
     convertMath: ->
       body = @$el.find(".response-body")
       body.html DiscussionUtil.postMathJaxProcessor DiscussionUtil.markdownWithHighlight body.text()
-      MathJax.Hub.Queue ["Typeset", MathJax.Hub, body[0]]
+      if MathJax?
+        MathJax.Hub.Queue ["Typeset", MathJax.Hub, body[0]]
 
     _delete: (event) =>
         @trigger "comment:_delete", event

common/static/coffee/src/discussion/views/thread_response_show_view.coffee

@@ -27,7 +27,8 @@ if Backbone?
     convertMath: ->
       element = @$(".response-body")
       element.html DiscussionUtil.postMathJaxProcessor DiscussionUtil.markdownWithHighlight element.text()
-      MathJax.Hub.Queue ["Typeset", MathJax.Hub, element[0]]
+      if MathJax?
+        MathJax.Hub.Queue ["Typeset", MathJax.Hub, element[0]]
 
     edit: (event) ->
         @trigger "response:edit", event

common/templates/mathjax_include.html

@@ -12,6 +12,7 @@
     tex2jax: {inlineMath: [ ['$','$'], ["\\(","\\)"]],
               displayMath: [ ['$$','$$'], ["\\[","\\]"]]}
   });
+  HUB = MathJax.Hub
 </script>
 %else:
 <script type="text/x-mathjax-config">
@@ -27,6 +28,7 @@
       ]
     }
   });
+  HUB = MathJax.Hub
 </script>
 %endif
 

lms/static/coffee/src/customwmd.coffee

@@ -2,11 +2,6 @@
 
 $ ->
 
-  if not MathJax?
-    return
-
-  HUB = MathJax.Hub
-
   class MathJaxProcessor
 
     MATHSPLIT = /// (
@@ -116,10 +111,11 @@ $ ->
     Markdown.getMathCompatibleConverter = (postProcessor) ->
       postProcessor ||= ((text) -> text)
       converter = Markdown.getSanitizingConverter()
-      processor = new MathJaxProcessor()
-      converter.hooks.chain "preConversion", MathJaxProcessor.removeMathWrapper(processor)
-      converter.hooks.chain "postConversion", (text) ->
-        postProcessor(MathJaxProcessor.replaceMathWrapper(processor)(text))
+      if MathJax?
+        processor = new MathJaxProcessor()
+        converter.hooks.chain "preConversion", MathJaxProcessor.removeMathWrapper(processor)
+        converter.hooks.chain "postConversion", (text) ->
+          postProcessor(MathJaxProcessor.replaceMathWrapper(processor)(text))
       converter
 
     Markdown.makeWmdEditor = (elem, appended_id, imageUploadUrl, postProcessor) ->

lms/static/coffee/src/mathjax_delay_renderer.coffee

@@ -57,7 +57,7 @@ class @MathJaxDelayRenderer
         @$buffer.html(text)
         curTime = getTime()
         @elapsedTime = curTime - prevTime
-        if MathJax
+        if MathJax?
           prevTime = getTime()
           @mathjaxRunning = true
           MathJax.Hub.Queue ["Typeset", MathJax.Hub, @$buffer.attr("id")], =>