coord trafo at Frame level, with 1st application to AxesInDifferentUnits

contributes to #702 (closed)

Base/Axis/FrameTrafo.h

+//  ************************************************************************************************
+//
+//  BornAgain: simulate and fit reflection and scattering
+//
+//! @file      Base/Axis/FrameTrafo.h
+//! @brief     Defines class FrameTrafo.
+//!
+//! @homepage  http://www.bornagainproject.org
+//! @license   GNU General Public License v3 or higher (see COPYING)
+//! @copyright Forschungszentrum Jülich GmbH 2018
+//! @authors   Scientific Computing Group at MLZ (see CITATION, AUTHORS)
+//
+//  ************************************************************************************************
+
+#ifndef BORNAGAIN_BASE_AXIS_FRAMETRAFO_H
+#define BORNAGAIN_BASE_AXIS_FRAMETRAFO_H
+
+#include <functional>
+#include <string>
+#include <vector>
+
+class Coordinate;
+
+using trafo_t = std::function<double(double)>;
+
+//! One specific transform of frame coordinates.
+
+class FrameTrafo {
+public:
+    ~FrameTrafo();
+    FrameTrafo* clone() const;
+    std::string name;
+    std::vector<Coordinate> coords;
+    std::vector<trafo_t> axTrafos;
+    bool xMirror{false};
+};
+
+#endif // BORNAGAIN_BASE_AXIS_FRAMETRAFO_H