Merged requested to merge olupton_template_tracklistmerger into master
TrackListMerger algorithm (which doesn't seem to be used anywhere) only accepted/produced
This MR turns it into a template and creates two instances, one using
LHCb::Track::Selection as before (now called
TrackSelectionMerger) and the other using
This is useful for feeding the MuonID (which expects one input location) in ZombieMoore Hlt2 (which keeps long/downstream tracks in separate locations).