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';
diff --git a/client/src/pages/AccountSettings.tsx b/client/src/pages/AccountSettings.tsx
index da631d3..35c0678 100644
--- a/client/src/pages/AccountSettings.tsx
+++ b/client/src/pages/AccountSettings.tsx
@@ -16,10 +16,10 @@
  * <https://www.gnu.org/licenses/>.
  */
 import { CircularProgress, Container } from '@mui/material';
+import { Account } from 'jami-web-common';
 import { useEffect, useState } from 'react';
 import { useParams } from 'react-router';
 
-import Account from '../../../model/Account';
 import { setAccountId, setAccountObject } from '../../redux/appSlice';
 import { useAppDispatch } from '../../redux/hooks';
 import authManager from '../AuthManager';
diff --git a/client/src/pages/Messenger.tsx b/client/src/pages/Messenger.tsx
index fa10cfd..1fd2252 100644
--- a/client/src/pages/Messenger.tsx
+++ b/client/src/pages/Messenger.tsx
@@ -16,11 +16,10 @@
  * <https://www.gnu.org/licenses/>.
  */
 import { Stack } from '@mui/material';
+import { Contact, Conversation } from 'jami-web-common';
 import { useEffect, useState } from 'react';
 import { useParams } from 'react-router';
 
-import Contact from '../../../model/Contact';
-import Conversation from '../../../model/Conversation';
 import { useAppSelector } from '../../redux/hooks';
 import authManager from '../AuthManager';
 //import Sound from 'react-sound';
diff --git a/client/src/pages/ServerConfiguration.tsx b/client/src/pages/ServerConfiguration.tsx
index 99e7547..56d06a8 100644
--- a/client/src/pages/ServerConfiguration.tsx
+++ b/client/src/pages/ServerConfiguration.tsx
@@ -17,10 +17,10 @@
  */
 import CircularProgress from '@mui/material/CircularProgress';
 import Container from '@mui/material/Container';
+import { Account } from 'jami-web-common';
 import { useEffect, useState } from 'react';
 import { useParams } from 'react-router-dom';
 
-import Account from '../../../model/Account';
 import authManager from '../AuthManager';
 import AccountPreferences from '../components/AccountPreferences';
 import Header from '../components/Header';