.make.eval.train.dexes accepting more methods

Hi,

I have added more methods to function .make.eval.train.dexes() that is part of CST_Calibration.R in https://earth.bsc.es/gitlab/external/cstools/-/tree/dev-cross-indices?ref_type=heads

I haven't checked if the method works with Calibration(). That would be good, but not sure if it is necessary. My objective is to directly use the function .make.eval.train.dexes(). I have also included some unit tests that could be expanded.

Núria