Complete "Hydrate Fallback".

Note: I checked in React DevTool that the Suspend and the fallback is present, but the skeleton of the page is already rendered into the server so that Suspend is impossible to trigger!
You can see it as it is during long load, o I will probably remove it in the next commit.

src/app/loading.tsx

@@ -0,0 +1,8 @@
+export default function Loading() {
+  return (
+    <div id="loading-splash">
+      <div id="loading-splash-spinner"/>
+      <p>Loading, please wait...</p>
+    </div>
+  );
+}