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/Models/Airline.php

@@ -96,4 +96,14 @@ class Airline extends Model
     {
         $this->attributes['icao'] = strtoupper($icao);
     }
+
+    public function flights()
+    {
+        return $this->belongsTo(Flight::class, 'airline_id');
+    }
+
+    public function pireps()
+    {
+        return $this->belongsTo(Pirep::class, 'airline_id');
+    }
 }