Cluster summary rewrite

The ClusterSummary and ClusterSummaryProducer classes were updated to improve performance, as documented here:

https://its.cern.ch/jira/browse/CMSTRACK-51
(https://indico.cern.ch/event/322710/session/5/contribution/2/material/slides/1.pdf)
@slava77 : We do have enum support for the CutStringParser, e.g. used in
https://github.com/cms-sw/cmssw/blob/CMSSW_7_2_X/PhysicsTools/PatAlgos/python/triggerLayer1/triggerMatcherExamples_cfi.py#L104
where `TriggerMuon` is an enum defined in
https://github.com/cms-sw/cmssw/blob/CMSSW_7_2_X/DataFormats/HLTReco/interface/TriggerTypeDefs.h#L53
and made available in
https://github.com/cms-sw/cmssw/blob/CMSSW_7_2_X/DataFormats/HLTReco/src/classes_def.xml#L37
I do not know the technicalities behind though.