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/ContactList.js b/client/src/components/ContactList.js
index 7da8375..d8e6add 100644
--- a/client/src/components/ContactList.js
+++ b/client/src/components/ContactList.js
@@ -1,11 +1,12 @@
+import { Person } from '@mui/icons-material';
+import { ListItem, ListItemAvatar, ListItemText } from '@mui/material';
 import List from '@mui/material/List';
+import { useEffect, useState } from 'react';
+import Modal from 'react-modal';
+
+import { useAppDispatch, useAppSelector } from '../../redux/hooks';
 import authManager from '../AuthManager';
 import ConversationAvatar from './ConversationAvatar';
-import Modal from 'react-modal';
-import { useState, useEffect } from 'react';
-import { Person } from '@mui/icons-material';
-import { useAppDispatch, useAppSelector } from '../../redux/hooks';
-import { ListItem, ListItemAvatar, ListItemText } from '@mui/material';
 
 const customStyles = {
   content: {