rename the GPC modular

@karlnapf 
this is a big patch.
I just test it at one shot.
I will send a PR for the notebook tomorrow since switching different branch is annoying when some error occurs in this PR 
Why should this field be there? If it's used only in multiclass case, probably it should be somewhere else. I think, that it's not good. For instance: CExactInferenceMethod class is inherited from CInferenceMethod class, but this field means nothing for CExactInferenceMethod class and it's not used there.