Re-add extensions as top level dir

extensions/ohif-vtk-extension/src/ToolbarModule.js

@@ -0,0 +1,15 @@
+import React, { Component } from 'react';
+import PropTypes from 'prop-types';
+import ConnectedToolbarSection from './ConnectedToolbarSection';
+
+class ToolbarModule extends Component {
+  render() {
+    return (
+      <div className="ToolbarModule">
+        <ConnectedToolbarSection />
+      </div>
+    );
+  }
+}
+
+export default ToolbarModule;