properly convert to the GT jet coordinate system

Make the conversion based on https://github.com/uwcms/UCT2015/blob/master/plugins/UCT2015GctCandsProducer.cc and https://github.com/cms-sw/cmssw/blob/CMSSW_7_1_X/DataFormats/L1CaloTrigger/interface/L1CaloRegionDetId.h