Draft: Allow Filter and ThOrCombiner to process neutrals

Adapt the ThOr combiner in such a way that it can process NeutralBasics modifying the vertex fitter accordingly. Define also an algorithm to make NeutralBasics out of the ECAL reconstruction container and a filter using Pr::Filter.

Depends on LHCb!3307 (closed), Rec!2639 (closed); used on Moore!1200 (closed)