Add base implementation of extendable events classes

Modified server deletion to use internal event handlers from the
Eloquent models themselves. Also added a few preliminary event handlers
in the `Pterodactyl\Events\<USer|Server> namespace that users can hook
into in EventServiceProvider to perform their own actions as they
please (such as push notifications and such).

app/Models/Node.php

@@ -26,9 +26,12 @@ namespace Pterodactyl\Models;
 
 use GuzzleHttp\Client;
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Notifications\Notifiable;
 
 class Node extends Model
 {
+    use Notifiable;
+
     /**
      * The table associated with the model.
      *