On login page, clear aircraft/airline fields if model is not from DB

* discussion https://swift-project.slack.com/archives/CCV74GESV/p1543344801126700
* emulated driver settings allow non DB model for testing
* use "showOverlayHTMLMessage"

src/blackgui/components/dbmodelkeycompleter.cpp

@@ -14,6 +14,7 @@
 #include <QCompleter>
 
 using namespace BlackCore;
+using namespace BlackMisc::Simulation;
 
 namespace BlackGui
 {
@@ -36,7 +37,7 @@ namespace BlackGui
             this->initCompleter();
         }
 
-        BlackMisc::Simulation::CAircraftModel CDbModelKeyCompleter::getAircraftModel() const
+        CAircraftModel CDbModelKeyCompleter::getAircraftModel() const
         {
             return sGui->getWebDataServices()->getModelForModelString(this->text().toUpper().trimmed());
         }