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)


so, I tried to enable the splitting and this function doesn't work, breaking on missing iter0TrackRefsForJets.

Andrea,
Please provide a function that can enable the code to show it at least runs.

Thank you.