Handle MPI communicator inside the environment
Refactor some code on the Simulation class
Handle most of MPI communications on Simulation base class
Remove old simulation class

The Simulation base class now handles most of the MPI communication among nodes. Now is
easiest to implement concrete simulation classes.
Put AceIsotope class in other compilation unit
Add AceIsotopeBase class

This class will represent a base interface for ACE isotopes. A new subclassing
should be done to handle different "types" of fission treatment, thermal treatment
and ptables for ACE isotopes.

Probably all this will be handled as policies
Get fission reaction from energy and RNG
Refactor code and add Fission treatment policy
Refactor isotope factory

Modify the isotope factory to create isotopes with different fission treatment
policies depending on the information in the NU block
Parse delayed neutron data from ACE table
Handle NU samlper on base FissionPolicy class
Parse delayed NU data when available
Initialize nu sampler pointers
Fix some memory leaks
Sample neutrons with delayed spectrum
Fix some memory issues