Fixes (#435)

* Add flight level field to PIREP field closes #401

* Default value for distance 0 closes #400

* Block airline deletion if assets exist #367

* Formatting

* Move some of the base exception classes

* Fix skin references to use settings table

* Set default for theme name if setting is wrong

app/Exceptions/AircraftNotAtAirport.php

@@ -7,7 +7,7 @@ use App\Models\Aircraft;
 /**
  * Class AircraftNotAtAirport
  */
-class AircraftNotAtAirport extends HttpException
+class AircraftNotAtAirport extends AbstractHttpException
 {
     public const MESSAGE = 'The aircraft is not at the departure airport';