Reclustering jets (cleaned up version)

As #143 but with some clean-up of the interface (after an email exchange with @clseitz):
   * inputs and outputs are 4-vectors
   * no `using namespace` in headers
   * output of the analyzer is `event.reclusteredFatJets` instead of just `event.fatJets` (which might otherwise suggest the fat jets from the miniAOD)

Validated against #143 on 2000 events of *T1tttt_2J_mGl1500_mLSP100* (about 4k fat jets), results are identical except for the mass which sometimes changes by 0.01 GeV, which is possibly because of roundoffs due to float precision in the original code.