Add `common` subproject containing shared files

Move classes in `model` to their own `common` package.
Now, the client and server can import `common` as a library.
This is the first step to eventually migrate all the source code at the root of the
project to an `old-server` package.

GitLab: #55
Change-Id: I4b7a52e80171d9c3399416ab524bcdd6915ac540
diff --git a/client/src/pages/AccountSelection.tsx b/client/src/pages/AccountSelection.tsx
index 86e0591..35aed97 100644
--- a/client/src/pages/AccountSelection.tsx
+++ b/client/src/pages/AccountSelection.tsx
@@ -18,10 +18,10 @@
 import { AddRounded } from '@mui/icons-material';
 import { Avatar, Card, CardHeader, Container, List } from '@mui/material';
 import { motion } from 'framer-motion';
+import { Account } from 'jami-web-common';
 import { Fragment, useEffect, useState } from 'react';
 import { useNavigate } from 'react-router';
 
-import Account from '../../../model/Account';
 import authManager from '../AuthManager';
 import ConversationAvatar from '../components/ConversationAvatar';
 import Header from '../components/Header';