put htmlmixed.js and css.js includes in CMS base.html so that we can support…

put htmlmixed.js and css.js includes in CMS base.html so that we can support html mode in CodeMirror

cms/templates/base.html

@@ -33,6 +33,8 @@
     <script src="${static.url('js/vendor/jquery.leanModal.min.js')}"></script>
     <script src="${static.url('js/vendor/jquery.tablednd.js')}"></script>
     <script src="${static.url('js/vendor/jquery.form.js')}"></script>
+    <script type="text/javascript" src="${static.url('js/vendor/CodeMirror/htmlmixed.js')}"></script>
+    <script type="text/javascript" src="${static.url('js/vendor/CodeMirror/css.js')}"></script>
     <script type="text/javascript">
       document.write('\x3Cscript type="text/javascript" src="' +
           document.location.protocol + '//www.youtube.com/player_api">\x3C/script>');

common/lib/xmodule/xmodule/js/src/html/edit.coffee

 class @HTMLEditingDescriptor
   constructor: (@element) ->
     @edit_box = CodeMirror.fromTextArea($(".edit-box", @element)[0], {
+      mode: "text/html"
       lineNumbers: true
       lineWrapping: true
     })