Merge Fennix branch to master

[leucinw]

FENNIX model is implemented for use with torsion OPT and SP calculations. Use keywords in poltype.ini file to enable

• toroptmethod=FENNIX
• torspmethod=FENNIX

Other combinations such as xtb+FENNIX, FENNIX+wB97X-D etc are also possible. Pre-trained NN models are located at fennixmodeldir and users can switch the model by using keyword fennixmodelname. Currently this can be set to the followings:

• fennixmodelname=ani2x_model0 # default
• fennixmodelname=ani2x_model1
• fennixmodelname=ani2x_model2