TTH/Susy python code: further refactoring and cleanup

Refactoring and cleanup to avoid copy-paste across files:
* move definition of common modules into **python/analyzers/susyCore_modules_cff.py** (cfgs cannot import from cfgs), so that each new cfg only has to reconfigure the skimmers and add its specific analyzers (if any) and its own tree producer
* modify the treeProducer class so that specific ones can inherit from the susyCore one and just add variables (or even remove them)

Others:
* add QG tagger and some extra PU id variables (from Mariarosaria) 
* make sure we don't filter on Higgs boson decay modes (important if we go to susy models that have Higgses)
* rename the SUSYGenStatusThree.py so that it follows a more consistent naming convention (and call the mother id *motherId* since *sourceId* was something different and that could have created confusion)