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/EditDiscussion.php

@@ -0,0 +1,50 @@
+<?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 EditDiscussion
+{
+    /**
+     * The ID of the discussion to edit.
+     *
+     * @var int
+     */
+    public $discussionId;
+
+    /**
+     * The user performing the action.
+     *
+     * @var \Flarum\User\User
+     */
+    public $actor;
+
+    /**
+     * The attributes to update on the discussion.
+     *
+     * @var array
+     */
+    public $data;
+
+    /**
+     * @param int $discussionId The ID of the discussion to edit.
+     * @param \Flarum\User\User $actor The user performing the action.
+     * @param array $data The attributes to update on the discussion.
+     */
+    public function __construct($discussionId, User $actor, array $data)
+    {
+        $this->discussionId = $discussionId;
+        $this->actor = $actor;
+        $this->data = $data;
+    }
+}