fix type of a lookup table/vector for channel order -> index

Investigated compile error with @reister. Changing the type of the variable whose entries are used as indices to Eigen::Vector3i solves the problem. Using Eigen::Matrix<size_t, 6, 1>, which seemed even more suitable, did not work.

source/RobotAPI/gui-plugins/FTSensorCalibrationGui/FTSensorCalibrationGuiWidgetController.h

@@ -175,7 +175,7 @@ namespace armarx
 
         Eigen::Matrix6f                   _conversion_matrix;
         Eigen::Vector6f                   _offset;
-        Eigen::Vector6f                   _channel_order;
+        Eigen::Vector6i                   _channel_order;
         float                             _ticks_to_volt_factor;
 
         RobotUnitDataStreamingReceiverPtr _streaming_handler;