Introduce VPFullCluster class

Introduction of a second VPClass named VPFullCluster which includes the vector among the private members. Needed to later fix the issue of tracking efficiencies for TDR->master merge.

FYI : @cattanem , @sponce, @gligorov , @sneubert , @sstahl, @chasse , @graven , @adudziak , @fpolci , @gdujany