updated css for dragonx theme and added as option to settings menu

src/firsttimewizard.cpp

@@ -36,7 +36,7 @@ void FirstTimeWizard::slot_change_theme(const QString& theme_name) {
     }
     catch (...)
     {
-        saved_theme_name = "Dark";
+        saved_theme_name = "dragonx";
     }
 
     QFile qFile(":/css/res/css/" + saved_theme_name +".css");