Massively simplify API binding logic

Changes the API internals to use normal Laravel binding which automatically supports nested-models and can determine their relationships. This removes a lot of confusingly complex internal logic and replaces it with standard Laravel code.

This also removes a deprecated "getModel" method and fully replaces it with a "parameter" method that does stricter type-checking.

tests/Traits/Http/IntegrationJsonRequestAssertions.php

@@ -20,7 +20,7 @@ trait IntegrationJsonRequestAssertions
                 [
                     'code' => 'NotFoundHttpException',
                     'status' => '404',
-                    'detail' => 'The requested resource does not exist on this server.',
+                    'detail' => 'The requested resource could not be found on the server.',
                 ],
             ],
         ], true);