added Overlap removal function (still need to actually put in the links)
requested to merge ancsmith/athena:LLP1_mergeLepContainers_OverlapRemoval into LLP1_mergeLepContainers
This adds the function which can be used to check if LRT and prompt electrons share clusters via a delta R match, before the track collections for prompt/LRT are merged. Saving the info that the clusters are overlapping via an ElementLink still needs to be done