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/ReadDiscussionHandler.php

@@ -0,0 +1,51 @@
+<?php namespace Flarum\Core\Discussions\Commands;
+
+use Flarum\Core\Discussions\DiscussionRepositoryInterface;
+use Flarum\Core\Discussions\Events\DiscussionStateWillBeSaved;
+use Flarum\Core\Exceptions\PermissionDeniedException;
+use Flarum\Core\Support\DispatchesEvents;
+
+class ReadDiscussionHandler
+{
+    use DispatchesEvents;
+
+    /**
+     * @var DiscussionRepositoryInterface
+     */
+    protected $discussions;
+
+    /**
+     * @param DiscussionRepositoryInterface $discussions
+     */
+    public function __construct(DiscussionRepositoryInterface $discussions)
+    {
+        $this->discussions = $discussions;
+    }
+
+    /**
+     * @param ReadDiscussion $command
+     * @return \Flarum\Core\Discussions\DiscussionState
+     * @throws \Flarum\Core\Exceptions\PermissionDeniedException
+     */
+    public function handle(ReadDiscussion $command)
+    {
+        $actor = $command->actor;
+
+        if (! $actor->exists) {
+            throw new PermissionDeniedException;
+        }
+
+        $discussion = $this->discussions->findOrFail($command->discussionId, $actor);
+
+        $state = $discussion->stateFor($actor);
+        $state->read($command->readNumber);
+
+        event(new DiscussionStateWillBeSaved($state));
+
+        $state->save();
+
+        $this->dispatchEventsFor($state);
+
+        return $state;
+    }
+}