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)


actually this part is not coming from me.... @rovere can you have a look?
it worked for me on the release I used for tests... perhaps something changed in the 73X trk config?