Fixes some React warnings.

frontend/src/App.js

@@ -1,5 +1,5 @@
 import './App.css';
-import React, { useState, useEffect } from 'react';
+import React, { useState, useEffect, useCallback } from 'react';
 import MenuBar from './components/MenuBar';
 import Login from './components/Login';
 import Gamenights from './components/Gamenights';
@@ -68,20 +68,20 @@ function App() {
     setFlashData(data);
   };
 
-  const refetchGamenights = () => {
+  const refetchGamenights = useCallback(() => {
     unpack_api_result(get_gamenights(user.jwt), setFlashData)
       .then(result => {
         if (result !== undefined) {
           setGamenights(result.gamenights);
         }
       }); 
-  };
+  }, [user]);
 
   useEffect(() => {
     if (appState === 'LoggedIn') {
       refetchGamenights()
     }
-  }, [appState])
+  }, [appState, refetchGamenights])
 
   useEffect(() => {
     if (appState === 'LoggedIn') {
@@ -92,7 +92,7 @@ function App() {
         }
       });
     }        
-  }, [appState])
+  }, [appState, user])
 
   useEffect(() => {
     setUser(JSON.parse(localStorage.getItem(localStorageUserKey)));

frontend/src/components/AdminPanel.jsx

@@ -1,4 +1,4 @@
-import {useState, useEffect} from 'react';
+import {useState, useEffect, useCallback} from 'react';
 import Checkbox from '@mui/material/Checkbox';
 import Table from '@mui/material/Table';
 import TableBody from '@mui/material/TableBody';
@@ -35,7 +35,7 @@ function AdminPanel(props) {
     setPage(0);
   };
 
-  const refetchTokens = () => {
+  const refetchTokens = useCallback(() => {
     if(props.user !== null) {
       unpack_api_result(get_registration_tokens(props.user.jwt), props.setFlash)
         .then(result => {
@@ -44,7 +44,7 @@ function AdminPanel(props) {
           }
         });
     } 
-  }
+  }, [props.setFlash, props.user]);
 
   const deleteToken = (id) => {
     if(props.user !== null) {
@@ -75,7 +75,7 @@ function AdminPanel(props) {
 
   useEffect(() => {
     refetchTokens()
-  }, [])
+  }, [refetchTokens])
 
   let columns = [
     {

frontend/src/components/Gamenight.jsx

@@ -1,4 +1,4 @@
-import React, { useState, useEffect } from 'react';
+import React, { useState, useEffect, useCallback } from 'react';
 import List from '@mui/material/List';
 import ListItem from '@mui/material/ListItem';
 import ListItemText from '@mui/material/ListItemText';
@@ -13,10 +13,10 @@ import {unpack_api_result, get_gamenight, patch_gamenight} from '../api/Api';
 
 function Gamenight(props) {
 
-  const [dense, setDense] = useState(true);
+  const dense = true;
   const [gamenight, setGamenight] = useState(null);
 
-  const fetchGamenight = () => {
+  const fetchGamenight = useCallback(() => {
     if (props.user !== null) {
       unpack_api_result(get_gamenight(props.gamenightId, props.user.jwt), props.setFlash)
         .then(result => {
@@ -25,9 +25,9 @@ function Gamenight(props) {
           }
         });
     }
-  }
+  }, [props.gamenightId, props.user, props.setFlash]);
 
-  useEffect(fetchGamenight, []);
+  useEffect(fetchGamenight, [fetchGamenight]);
 
   let games = gamenight?.game_list.map(g =>
     (

frontend/src/components/Gamenights.jsx

@@ -12,7 +12,7 @@ import AddGameNight from './AddGameNight';
 import {delete_gamenight, unpack_api_result} from '../api/Api';
 
 function Gamenights(props) {
-  const [dense, setDense] = React.useState(false);
+  const dense = true;
 
   const DeleteGamenight = (game_id) => {
     if (props.user !== null) {