Move command classes to domain namespaces

They will probably be refactored away at a later stage (when we get
rid of the command bus). Until then, this lets us remove the
Flarum\Core namespace and actually feels quite clean.

src/Discussion/Command/StartDiscussion.php

@@ -0,0 +1,42 @@
+<?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\Discussion\Command;
+
+use Flarum\User\User;
+
+class StartDiscussion
+{
+    /**
+     * The user authoring the discussion.
+     *
+     * @var User
+     */
+    public $actor;
+
+    /**
+     * The discussion attributes.
+     *
+     * @var array
+     */
+    public $data;
+
+    /**
+     * @param User $actor The user authoring the discussion.
+     * @param array $data The discussion attributes.
+     */
+    public function __construct(User $actor, array $data, $ipAddress)
+    {
+        $this->actor = $actor;
+        $this->data = $data;
+        $this->ipAddress = $ipAddress;
+    }
+}