Updated markdown preview to update on diff-basis

Uses vdom system to diff and update the current markdown preview view
instead of requiring a full HTML replace change.
This should provide better performance, expecially where dynamically
loaded content such as iframes were in use.

Closes #3454

resources/js/services/vdom.js

@@ -0,0 +1,31 @@
+import {
+    init,
+    attributesModule,
+    toVNode
+} from "snabbdom";
+
+let patcher;
+
+/**
+ * @returns {Function}
+ */
+function getPatcher() {
+    if (patcher) return patcher;
+
+
+    patcher = init([
+        attributesModule,
+    ]);
+
+    return patcher;
+}
+
+/**
+ * @param {Element} domTarget
+ * @param {String} html
+ */
+export function patchDomFromHtmlString(domTarget, html) {
+    const contentDom = document.createElement('div');
+    contentDom.innerHTML = html;
+    getPatcher()(toVNode(domTarget), toVNode(contentDom));
+}