move CovarianceEstimator to Rec
Move CaloFuture/CaloFutureUtils/CaloFutureUtils/CovarianceEstimator from LHCb to Rec to simplify future changes.
note: CovarianceEstimator is only used inside CaloFuture/CaloFutureReco, hence that is where it will now reside.
To be applied in conjunction with Rec!2046 (merged) which adds CovarianceEstimator to Rec.
Edited by Gerhard Raven