xAODTau: add a lightweight EDM, TauCluster
Add TauCluster, which contains the four momentum pointing at the tau vertex, dR w.r.t the tau axix, and an ElementLink to the original CaloCluster used in jet reconstrution. The original link to the CaloCluster is removed since it is not used at all.
After this MR is merged, we could associate the TauCluster to the tau candidate, so that we do not need to obtain the clusters from scratch and perform the vertex correction every time !