added rotate around point function

src/core/math/RotationFunctions.h

+//======================================================================================================================
+//
+//  This file is part of waLBerla. waLBerla is free software: you can
+//  redistribute it and/or modify it under the terms of the GNU General Public
+//  License as published by the Free Software Foundation, either version 3 of
+//  the License, or (at your option) any later version.
+//
+//  waLBerla is distributed in the hope that it will be useful, but WITHOUT
+//  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+//  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+//  for more details.
+//
+//  You should have received a copy of the GNU General Public License along
+//  with waLBerla (see COPYING.txt). If not, see <http://www.gnu.org/licenses/>.
+//
+//! \file RotationFunctions.h
+//! \author Sebastian Eibl <sebastian.eibl@fau.de>
+//
+//======================================================================================================================
+
+#pragma once
+
+#include <core/math/Rot3.h>
+#include <core/math/Vector3.h>
+
+namespace walberla {
+namespace math {
+
+template< typename Type >
+inline void rotateAroundPoint( Vector3<Type>& pos,
+                               Rot3<Type>& rot,
+                               const Vector3<Type>& rotateAround,
+                               const Rot3<Type>& dRot )
+{
+   const auto dp = pos - rotateAround;
+   pos = rotateAround + dRot.getMatrix() * dp;
+   rot.rotate(dRot);
+}
+
+} // mpi
+} // walberla