This corresponds to the managment of the files proposing several models for one protein, such as produced by NMR studies. The driving idea is that only one model is considered at one time for one PDB instance. This could certainly be improved. Two facilities are implemented:
nModels(): will return the number of models of the PDB instance.
setModel(model number, verbose):
This will install the model of rank specified by ``model number''
as the current working set.