Initial version of ATLFAST3F_ACTSMT Simulator

ATLFAST3F_ACTSMT uses Acts Fatras for the Inner Detector/ITk, FastCaloSimV2/FastCaloGAN (otherwise Geant4) in the Calorimeters and Geant4 in the Muon System. It is based on SimKernelMT and is therefore intended to be compatible with AthenaMT running. Further development is required to complete the interface between Acts Fatras and the ISF before it can be properly tested though.

Adding this now to allow Acts Fatras to be run without needing to also support FastCaloSim V1 (as used in ATLFASTII).

Tagging @rwang, @fatsai, @pagacova, @cyoung, @zhangr, @mbandier, @schaarsc, @tlari