Sort imports from all files

Add "prettier" script in `package.json` to check if all files are
compliant.

Sort all imports and format all files by running `npm run lint -- --fix`
followed by `npm run prettier -- --write`.

Gitlab #29

Change-Id: Id80402d1344c3bc611f66a46cffeee5f2c375bd8
diff --git a/client/src/components/ConversationList.js b/client/src/components/ConversationList.js
index 38628ad..e25dd9c 100644
--- a/client/src/components/ConversationList.js
+++ b/client/src/components/ConversationList.js
@@ -1,11 +1,12 @@
-import List from '@mui/material/List';
-import { useEffect } from 'react';
-import ConversationListItem from './ConversationListItem';
-import ListSubheader from '@mui/material/ListSubheader';
-import Conversation from '../../../model/Conversation';
 import { GroupRounded as GroupIcon } from '@mui/icons-material';
+import List from '@mui/material/List';
+import ListSubheader from '@mui/material/ListSubheader';
 import Typography from '@mui/material/Typography';
+import { useEffect } from 'react';
+
+import Conversation from '../../../model/Conversation';
 import { useAppSelector } from '../../redux/hooks';
+import ConversationListItem from './ConversationListItem';
 
 export default function ConversationList(props) {
   const { refresh } = useAppSelector((state) => state.app);