Add a DataContainer.add_ensemble_parameters function
The ensemble parameters needs to be set in each Ensemble before super init is called.
This can sometimes become a bit tricky and a dc.add_ensemble_parameter()
could be useful. Suggestion powered by @angqvist.
This would lead to unification of the three different ways (in four different ensembles) of obtaining the current atom counts in the atoms object.
Edited by Erik Fransson