calc_management insufficiently checks input values for B_LU_BRP, B_SOILTYPE_AGR and B_GWL_CLASS

[BrentWHR]

The inputs for this function are checked elsewhere when calc_management() is called by the wrapper function so it should not be a problem when OBIC is used normally.
Checkmates should be added to check B_LU_BRP values occur in crops.obic, GWL_CLASS values are from a restricted set of options (all prefixed by "Gt", and B_SOILTYPE_AGR must exist in OBIC::soils.obic$soiltype.