Added Pythia8 status code for intermediate resonances to the GenJets particle selector

Fix for the issue originally reported in https://hypernews.cern.ch/HyperNews/CMS/get/jet-algorithms/307.html The following changes were implemented:

- added Pythia8 status code for intermediate resonances so that GenJets 
in Pythia6 and Pythia8 samples behave the same way 

- moved b' (pdgId=7) from partons to resonances (I don't really know why 
b' was considered as parton in the first place)

- there is a pointer sorting step in the code which makes sense from the 
point of view of efficient searching through the linked list of 
GenParticles (and this is done quite frequently in the code) but there is no
protection against changing the particle 
order wrt the original GenParticle collection after pointer sorting is 
performed in a separate vector. The increase in timing that results from the added 
protection is not very significant (~3%).