Missing Particle Flow Proxy Builders

[alja]

There are the following PB in the Legacy Fireworks that can be migrated to FireworksWeb:

reco::PFCluster for projected views
https://github.com/cms-sw/cmssw/blob/master/Fireworks/ParticleFlow/plugins/FWPFClusterRPZProxyBuilder.cc

reco::PFBlock for projected views
https://github.com/cms-sw/cmssw/blob/master/Fireworks/ParticleFlow/plugins/FWPFBlockProxyBuilder.cc

Note: this issue is created based on discussions in issue #127