refs #755, mapping UI improvements

* make drop area more obvious by icon and color
* improve forms so the layout looks better on large screens
* button to display model dialog (like distributor, ICAO, ...)

src/blackgui/components/dbmappingcomponent.h

@@ -187,6 +187,9 @@ namespace BlackGui
             //! Stash models
             void stashSelectedModels();
 
+            //! Open model modify dialog
+            void modifyModelDialog();
+
         signals:
             //! Request to filter by livery
             void filterByLivery(const BlackMisc::Aviation::CLivery &livery);
@@ -273,9 +276,6 @@ namespace BlackGui
             //! Apply current DB data from form
             void ps_applyFormDistributorData();
 
-            //! Open model modify dialog
-            void ps_modifyModelDialog();
-
             //! Add to own model set
             void ps_addToOwnModelSet();