PCBT klfitter fro ttbb analysis

Implementation of KLFitter for all-had ttbb analysis. An existing version of our iterative KLFitter implementation had been already merged into 21.2. After the merge, we had to adjust our implementation further so that the pseudo-continuous b-tagging is used for ordering jets prior to the KLFitter run. In the previous version, the b-tagging weight was used for jet ordering, which was not supported by the flavour tagging group. The ordering using pseudo-continuous b-tagging is added as an additional option. The ordering using the weight has been kept, but a WARNING added explaining that this method is not supported by flavour tagging.