Move template in-class function definitions out of class

Keeping them defined in-class caused linker issues with the extern template
declaration in a non-optimized MinGW debug build. Apparently it did not
inline them but instead relied on the extern declaration and expected
them defined somewhere else.

src/blackmisc/simulation/interpolator.h

@@ -227,7 +227,7 @@ namespace BlackMisc
             void initCorrespondingModel(const CAircraftModel &model = {});
 
             //! Mark as unit test
-            void markAsUnitTest() { m_unitTest = true; }
+            void markAsUnitTest();
 
         protected:
             //! Constructor