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/Server.php

@@ -26,11 +26,12 @@ namespace Pterodactyl\Models;
 
 use Auth;
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Notifications\Notifiable;
 use Illuminate\Database\Eloquent\SoftDeletes;
 
 class Server extends Model
 {
-    use SoftDeletes;
+    use Notifiable, SoftDeletes;
 
     /**
      * The table associated with the model.