Various editor fixes (#160)

* Tab should move to body from heading

* Focus editor on mount, closes #156

* Closes #154 - Just went for the simple approach here, considered something more complex but this is clear

* Added body placeholder

frontend/scenes/Document/Document.js

@@ -167,7 +167,7 @@ type Props = {
     const isNew = this.props.newDocument;
     const isEditing = !!this.props.match.params.edit || isNew;
     const isFetching = !this.document;
-    const titleText = get(this.document, 'title', 'Loading');
+    const titleText = get(this.document, 'title', '');
     const document = this.document;
 
     return (