Improve the error message when markers are missing to calibrate/reconstruct a model

[Alzathar]

Currently if a marker is missing during the calibration or the reconstruction of a model, you can such kind of error message:
xyzModel - Missing landmarks to define the arm. Calibration aborted

It does not mention the side of the segment nor the missing marker(s). A better message could be:
xyzModel - Missing landmarks 'L.AC' and 'L.GH' to define the segment 'L.Arm'. Calibration aborted

Markers' name have to be the external names used (i.e. the name in the Trial object)