* Updating EventGeneratorIsotropic to allow simulation of higher

* multiplicities for an event. A new token 'Multiplicity=' has been
* created that is given to m_Multiplicity. In the function GenerateEvent
* a loop on m_Multiplicity is done for a given event. The
* check_Multiplicty is not require in order to not break any use of
* NPTool. The default value of m_Multiplicty being 1.