Updated codemirror to v4.12.

Did a lot of cleanup to limit the size of the plugin.
I kept the emmet plugin.

applications/admin/static/codemirror/mode/markdown/index.html

@@ -16,12 +16,12 @@
       .cm-s-default .cm-trailing-space-new-line:before {position: absolute; content: "\21B5"; color: #777;}
     </style>
 <div id=nav>
-  <a href="http://codemirror.net"><img id=logo src="../../doc/logo.png"></a>
+  <a href="http://codemirror.net"><h1>CodeMirror</h1><img id=logo src="../../doc/logo.png"></a>
 
   <ul>
     <li><a href="../../index.html">Home</a>
     <li><a href="../../doc/manual.html">Manual</a>
-    <li><a href="https://github.com/marijnh/codemirror">Code</a>
+    <li><a href="https://github.com/codemirror/codemirror">Code</a>
   </ul>
   <ul>
     <li><a href="../index.html">Language modes</a>