Started adding the code for the hybrid clustering algorithm. The classes that
are relevant to this feature are the ones containing a 'Cluster' in their name:
PvmClusterDataCore -> extends PvmDataCore and adds the information about cluster belogness.
PvmClusterDataCoreSplitter -> does the cluster splitting to reduce aberration of the average deviations
PvmClusterSolver-> calls the PvmClusterSystem and the PvmClusterDataCoreSplitter
PvmClusterSystem-> builds the cplex system for the cluster case and solves it