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

resources/views/mail/admin/user/registered.blade.php

@@ -0,0 +1,9 @@
+@component('mail::message')
+A new user has signed up!
+
+Name: {{ $user->name }}!
+Email: {{ $user->email }}
+State: {{ UserState::label($user->state) }}
+
+{{ config('app.name') }}
+@endcomponent