added TrackClassifierTool (TCT) to FlavorTagDiscriminants pkg

The TrackClassifierTool (TCT) is a feed forward neural network trained on the task of discriminating heavy flavor tracks for others (as defined in https://gitlab.cern.ch/atlas/athena/-/blob/master/PhysicsAnalysis/TrackingID/InDetTrackSystematicsTools/Root/InDetTrackTruthOriginTool.cxx). The tool is implemented under the FlavorTagDiscriminants package as a result of a discussion in Jira (https://its.cern.ch/jira/browse/AFT-595). The new files where the tool is effectively implemented are Root/TrackClassifier.cxx, FlavorTagDiscriminants/TrackClassifier.h and FlavorTagDiscriminants/ITrackClassifier.h.