Jet Core pixel cluster splitter

This is a first version of the jetcore cluster splitter (removing most of the debugging code, e.g. MC truth access).

This PR doesn't add anything to reco sequence yet but a customize function is made available for tests (timing, performance, tunining)


are these 1.3 and 1.9 some fundamental constants that would never change or some tuned parameters?
In the latter case, please introduce a parameter/constant