WIP: Tool for decorating ID tracks with a covariance matrix

This tool can be used to decorate ID tracks with a covariance matrix, according to some criteria, for writing into DAODs. The eventual aim is to drop the full covariance from the tracks at DAOD level and instead rely on these decorations, for which the full matrix would only be written for a small subset of tracks. Since the criteria for writing or not writing the covariance is not yet agreed (currently it is association with a primary vertex) and since it is not yet clear whether decoration with a new matrix or modification of the existing one is the best approach, this is left as WIP for now.