Streamline LHCbIDOverlapRelationTable.cpp

• simplify getting of LHCbIDs (one loop instead of up to three loops)
• sort LHCbIDs so that comparing will be O(N1+N2) instead of O(N1*N2)
• avoid creating a vector, only to use its size -- use LHCb::CountIterator instead.
• semantically an std::optional of a pointer does not make sense - use pointer instead.