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)


I'll have a look into this. Strangely enough, it worked also for Matti who did some very very preliminary tests on timing. 
@slava77 would you mind telling me exactly where and what did you test? I'll start from any recent IB in any case.

Ciao,
M.