Massive refactor

- Use contextual namespaces within Flarum\Core
- Clean up and docblock everything
- Refactor Activity/Notification blueprint stuff
- Refactor Formatter stuff
- Refactor Search stuff
- Upgrade to JSON-API 1.0
- Removed “addedPosts” and “removedPosts” relationships from discussion
API. This was used for adding/removing event posts after renaming a
discussion etc. Instead we should make an additional request to get all
new posts

Todo:
- Fix Extenders and extensions
- Get rid of repository interfaces
- Fix other bugs I’ve inevitably introduced

src/Core/Discussions/Commands/StartDiscussion.php

@@ -0,0 +1,30 @@
+<?php namespace Flarum\Core\Discussions\Commands;
+
+use Flarum\Core\Users\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)
+    {
+        $this->actor = $actor;
+        $this->data = $data;
+    }
+}