Add loading state (#1027)

* add loading state

* update snapshots

* add border radius

* fix comment breaking build jsx

src/components/LoadingMessage.tsx

@@ -0,0 +1,10 @@
+import React from "react";
+
+export const LoadingMessage = () => {
+  // !! KEEP THIS IN SYNC WITH index.html !!
+  return (
+    <div className="LoadingMessage">
+      <span>Loading scene...</span>
+    </div>
+  );
+};