Fixed headings hierarchy updates - fixes #3

The hierarchy now updates whenever the DOM changes

src/helpers/components/HeadingsHierarchy.js

@@ -9,7 +9,7 @@ import renderIf from 'render-if';
  *
  */
 const HeadingsHierarchy = ({items}) => (
-	<div className="HeadingsHierarchy Widget">
+	<div className="HeadingsHierarchy Widget" aria-live="polite">
 		<h4 className="HeadingsHierarchy-title">
 			<FormattedMessage id="HeadingsHierarchy.title" />
 		</h4>

src/helpers/helpers/headingsHierarchy.js

@@ -1,10 +1,27 @@
+import {debounce} from 'lodash';
 import {sendMessage} from '../../common/api/runtime';
 import getHeadingsHierarchy from '../api/getHeadingsHierarchy';
 import {GET} from '../actions/headingsHierarchy';
 import HeadingsHierarchyContainer from '../components/HeadingsHierarchyContainer';
 
 
 
+/**
+ *
+ */
+const sendHierarchy = () =>
+	sendMessage({
+		type: GET,
+		payload: getHeadingsHierarchy()
+	});
+
+/**
+ *
+ */
+const observer = new MutationObserver(
+	debounce(sendHierarchy, 300)
+);
+
 /**
  *
  */
@@ -23,13 +40,15 @@ export const describe = (intl) =>
  *
  */
 export const apply = () => {
-	sendMessage({
-		type: GET,
-		payload: getHeadingsHierarchy()
+	sendHierarchy();
+	observer.observe(document.body, {
+		childList: true
 	});
 };
 
 /**
  *
  */
-export const revert = () => {};
+export const revert = () => {
+	observer.disconnect();
+};