fixes #1236

- split up deprecated and remaining user notification logic
- started building a test (needs work)
- created new Model for NotificationPreference
- created extender to register a NotificationChannel
- created extender to maintain UserPreferences

User preferences are still possible on the users table directly.
Registering a user preference allows for transformation to happen.
And provides easier accessors. Not sure we want this.

! tests need work.

tests/integration/extenders/NotificationChannelTest.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Flarum\Tests\integration\extenders;
+
+use Flarum\Extend\NotificationChannel;
+use Flarum\Extend\UserPreferences;
+use Flarum\Tests\integration\RetrievesAuthorizedUsers;
+use Flarum\Tests\integration\TestCase;
+use Flarum\User\User;
+use Illuminate\Support\Arr;
+
+class NotificationChannelTest extends TestCase
+{
+    use RetrievesAuthorizedUsers;
+
+
+    public function setUp()
+    {
+        parent::setUp();
+
+        $this->prepareDatabase([
+            'users' => [
+               $this->normalUser()
+            ]
+        ]);
+    }
+
+    private function add_channel()
+    {
+        $this->extend(new NotificationChannel('test'));
+    }
+
+    /**
+     * @test
+     */
+    public function can_add_notification_channel()
+    {
+        $this->add_channel();
+
+        /** @var User $user */
+        $user = User::find(2);
+
+    }
+}

tests/integration/extenders/UserPreferencesTest.php

@@ -0,0 +1,61 @@
+<?php
+
+namespace Flarum\Tests\integration\extenders;
+
+use Flarum\Extend\UserPreferences;
+use Flarum\Tests\integration\RetrievesAuthorizedUsers;
+use Flarum\Tests\integration\TestCase;
+use Flarum\User\User;
+use Illuminate\Support\Arr;
+
+class UserPreferencesTest extends TestCase
+{
+    use RetrievesAuthorizedUsers;
+
+
+    public function setUp()
+    {
+        parent::setUp();
+
+        $this->prepareDatabase([
+            'users'            => [
+               $this->normalUser()
+            ]
+        ]);
+    }
+
+    private function add_preference()
+    {
+        $this->extend(
+            (new UserPreferences())
+                ->add('test', 'boolval', false)
+        );
+    }
+
+    /**
+     * @test
+     */
+    public function can_add_user_preference()
+    {
+        $this->add_preference();
+
+        /** @var User $user */
+        $user = User::find(2);
+        $this->assertEquals(false, Arr::get($user->preferences, 'test'));
+    }
+
+    /**
+     * @test
+     */
+    public function can_store_user_preference()
+    {
+        $this->add_preference();
+
+        /** @var User $user */
+        $user = User::find(2);
+
+        $user->setPreference('test', true);
+
+        $this->assertEquals(true, $user->test);
+    }
+}