feat: Replace SessionStorage with LocalStorage

frontend/src/components/app.tsx

@@ -36,7 +36,6 @@ interface IProps {
     setUserScoreDelta: (delta: number) => void;
 };
 
-// TODO: Replace the sessionStorage with localStorage?
 export default class Application extends React.Component<IProps> {
     componentDidMount() {
         // TODO: When asking the server if our session is still valid, a spinner