Add xbb tagger score in AT

This MR is adding the XbbTagger probabilities and score to TopAnalysis EventSaverFlatNtuple. An option in TopConfig has been added to enable the saving of these branches.

This option works fine with AntiKt10LCTopoTrimmedPtFrac5SmallR20Jets.

Any suggestion on how to improve it are very welcome.

Tagging TopReco conveners @omajersk @ravinab @tdado

Cheers, Valentina