Rename frontend directory (#472)

* Rename directory

* Cleanup

* Recover lost images

* remove lint

frontend/src/pages/NotFound.tsx

@@ -0,0 +1,14 @@
+function NotFound() {
+  return (
+    <div
+      style={{
+        display: "flex",
+        flex: 1,
+      }}
+    >
+      404 page not found
+    </div>
+  );
+}
+
+export default NotFound;