Use Notification/Notifiable (#379)

* Add migrations for notifiables

* Configure spatie-backup to run as part of cron

* Convert Mailer to Notification; add pirep notifications

* Styling

app/Notifications/Backups.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace App\Notifications;
+
+use Illuminate\Notifications\Notifiable;
+
+class Backups
+{
+    use Notifiable;
+
+    public function routeNotificationForMail()
+    {
+        return setting('general.admin_email');
+    }
+
+    public function routeNotificationForSlack()
+    {
+        return config('backup.notifications.slack.webhook_url');
+    }
+
+    public function getKey()
+    {
+        return 1;
+    }
+}