Rework sessions, remember cookies, and auth again

- Use Symfony's Session component to work with sessions, instead of a custom database model. Separate the concept of access tokens from sessions once again.
- Extract common session/remember cookie logic into SessionAuthenticator and Rememberer classes.
- Extract AuthenticateUserTrait into a new AuthenticationResponseFactory class.
- Fix forgot password process.

src/Http/Middleware/RememberFromCookie.php

@@ -0,0 +1,40 @@
+<?php
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Http\Middleware;
+
+use Flarum\Http\AccessToken;
+use Psr\Http\Message\ResponseInterface as Response;
+use Psr\Http\Message\ServerRequestInterface as Request;
+use Zend\Stratigility\MiddlewareInterface;
+
+class RememberFromCookie implements MiddlewareInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function __invoke(Request $request, Response $response, callable $out = null)
+    {
+        $id = array_get($request->getCookieParams(), 'flarum_remember');
+
+        if ($id) {
+            $token = AccessToken::find($id);
+
+            if ($token) {
+                $token->touch();
+
+                $session = $request->getAttribute('session');
+                $session->set('user_id', $token->user_id);
+            }
+        }
+
+        return $out ? $out($request, $response) : $response;
+    }
+}