Ref T225, force stylesheet in CForm base class and used by all forms

* Allows to use stylesheet attributes like [readonly]
* changing to "readonly" applies correct stylesheet

src/blackgui/editors/aircraftmodelform.cpp

@@ -32,6 +32,7 @@ namespace BlackGui
             ui->editor_AircraftIcao->setReadOnly(readOnly);
             ui->editor_Distributor->setReadOnly(readOnly);
             ui->editor_Livery->setReadOnly(readOnly);
+            this->forceStyleSheetUpdate();
         }
 
         void CAircraftModelForm::setSelectOnly()