Make templates work with nonempty baseUrls (e.g., IIS virtual directories)

templates/ReactSpa/ClientApp/boot.tsx

@@ -10,9 +10,10 @@ let routes = RoutesModule.routes;
 function renderApp() {
     // This code starts up the React app when it runs in a browser. It sets up the routing
     // configuration and injects the app into a DOM element.
+    const baseUrl = document.getElementsByTagName('base')[0].getAttribute('href');
     ReactDOM.render(
         <AppContainer>
-            <BrowserRouter children={ routes } />
+            <BrowserRouter children={ routes } basename={ baseUrl } />
         </AppContainer>,
         document.getElementById('react-app')
     );