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/addon/fold/foldgutter.js

@@ -1,3 +1,6 @@
+// CodeMirror, copyright (c) by Marijn Haverbeke and others
+// Distributed under an MIT license: http://codemirror.net/LICENSE
+
 (function(mod) {
   if (typeof exports == "object" && typeof module == "object") // CommonJS
     mod(require("../../lib/codemirror"), require("./foldcode"));
@@ -55,7 +58,7 @@
   function marker(spec) {
     if (typeof spec == "string") {
       var elt = document.createElement("div");
-      elt.className = spec;
+      elt.className = spec + " CodeMirror-guttermarker-subtle";
       return elt;
     } else {
       return spec.cloneNode(true);
@@ -64,14 +67,16 @@
 
   function updateFoldInfo(cm, from, to) {
     var opts = cm.state.foldGutter.options, cur = from;
+    var minSize = cm.foldOption(opts, "minFoldSize");
+    var func = cm.foldOption(opts, "rangeFinder");
     cm.eachLine(from, to, function(line) {
       var mark = null;
       if (isFolded(cm, cur)) {
         mark = marker(opts.indicatorFolded);
       } else {
-        var pos = Pos(cur, 0), func = opts.rangeFinder || CodeMirror.fold.auto;
+        var pos = Pos(cur, 0);
         var range = func && func(cm, pos);
-        if (range && range.from.line + 1 < range.to.line)
+        if (range && range.to.line - range.from.line >= minSize)
           mark = marker(opts.indicatorOpen);
       }
       cm.setGutterMarker(line, opts.gutter, mark);