Add ignore option for class names (#1555)

* Add ignore option for class names

This change adds another option for ignoring nodes for rendering similar to `ignoreTags`.
The new option `ignoreClasses` can hold an array of strings representing class names that should be ignored if they are in a node's class list. This can be desirable in dynamic environments.

* Adhere to CI rules for styling

* Add documentation for new option

* Exchange classList property with IE9 compatible code

* Harmonize variable names

* Add default for ignoredClasses

contrib/auto-render/auto-render.js

@@ -61,8 +61,11 @@ const renderElem = function(elem, optionsCopy) {
             elem.replaceChild(frag, childNode);
         } else if (childNode.nodeType === 1) {
             // Element node
+            const className = ' ' + childNode.className + ' ';
             const shouldRender = optionsCopy.ignoredTags.indexOf(
-                childNode.nodeName.toLowerCase()) === -1;
+                childNode.nodeName.toLowerCase()) === -1 &&
+                    optionsCopy.ignoredClasses.every(
+                        x => className.indexOf(' ' + x + ' ') === -1);
 
             if (shouldRender) {
                 renderElem(childNode, optionsCopy);
@@ -90,6 +93,8 @@ const defaultAutoRenderOptions = {
         "script", "noscript", "style", "textarea", "pre", "code",
     ],
 
+    ignoredClasses: [],
+
     errorCallback: function(msg, err) {
         console.error(msg, err);
     },