add calibration parameters in separate xacro files
in urdf/shoulder_v0/shoulder.urdf.xacro, we detect if parameters shoulder_pan_calibi, upper_arm_roll_calib equal to 0.
If equal, use the default values. If not equal, use the passing values.
We use this change on our system and to the best of my knowledge this is fully backward-compatible.
If anyone finds problems with this, please report them here and we can deal with them right away.