Labels of field monitors

Currently, when a field monitor is created, the labels "EField", "HField" or "Farfield" are used. The reason for this is that these are the keywords required by the VBA code for creating this monitors. Nevertheless, if these labels are used, then it is not possible to retrieve its results using the results retrieving methods, which expect labels like "e-field", "h-field" and "farfield".

This issue has been detected when creating the patch antenna example in #24 (closed) .