MET TST Systematics Pre-Recs

This MR updates the default paths of the METSystematicTool to point to the ones of the R22 pre-recommendations. In addition, two adjustments from R21 are propagated:

1. adding a protection for events where no object is added to the MET calculation and the MET consistent of only the soft term
2. adjust the MET TST systematic name to the __1up and __1down scheme

Tagging @hpacey, @aoneill & @gotero.