refs #911, allow to set model dir relative to simulator directory

* utility functions in simulator info
* and fscommonutil
* and button in UI to set default

src/blackmisc/simulation/simulatorinfo.cpp

@@ -111,6 +111,11 @@ namespace BlackMisc
             return isMicrosoftSimulator() || p3d();
         }
 
+        bool CSimulatorInfo::isFsxFamily() const
+        {
+            return fsx() || p3d();
+        }
+
         int CSimulatorInfo::numberSimulators() const
         {
             int c = fs9() ? 1 : 0;