Move generic util into lib

Might come in handy for the admin section later on

js/lib/utils/extractText.js

@@ -0,0 +1,19 @@
+/**
+ * Extract the text nodes from a virtual element.
+ *
+ * @param {VirtualElement} vdom
+ * @return {String}
+ */
+export default function extractText(vdom) {
+  let text = '';
+
+  if (vdom instanceof Array) {
+    text += vdom.map(element => extractText(element)).join('');
+  } else if (typeof vdom === 'object') {
+    text += extractText(vdom.children);
+  } else {
+    text += vdom;
+  }
+
+  return text;
+}