Removed member m_ToolAxis from mitk::NavigationTool and replaced it with a more general concept. The main axis of a tool is now defined as the negative z-axis of the tool coordinate system During tool calibration the user can calibrate an arbitrary tool axis. Call of SetToolAxis() given that calibrated axis will then result in the calculation of a ToolAxisTransform used to correctly align the tool coordinate system with respect to representation objects (e.g. surfaces) of the tool.