API for turning off subtraction of wave amplitudes on nonreflecting boundaries
- add API to CharacteristicBCBuilder to turn off wave amplitude subtraction on nonreflecting boundaries, as we have found is best for LBMS and Wasatch
- as discussed with James, this will likely break LBMS because this puts an argument in front of patchID, so LBMS will have to be fixed before this can be merged.