ENH: Include .H file, allows out of library derivation.

src/lagrangian/intermediate/submodels/Kinematic/CollisionModel/PairCollision/WallModel/WallModel/WallModel.H

@@ -39,6 +39,7 @@ SourceFiles
 #include "IOdictionary.H"
 #include "autoPtr.H"
 #include "runTimeSelectionTables.H"
+#include "WallSiteData.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //