FBT

FBT changes with some corrections regarding the beta-function weighting of the kicks. ExponentialDamper class was completely wrong (only a resistive damper with a reactive part always being set to 0) and no beta function weighting of the kick (equivalent to assuming that beta functions are always equal to 1). Beta function weighting in the kick of the FIR damper was also absent, which meant that the gain was not exactly equal to 2/(damping time in turns).