- Implement useful functionality from run_verify
  e.g. start_date, end_date, years_skip
- Include check functions for function arguments
- Include set_print_prt and set_time_sim
- Update set_print_prt to consider wb_sft case
  which needs basin_wb_aa output to be written

- Tested current state of softcal routine

- water balance softcal files are now in extdata folder
- water yield and baseflow fractions are now input arguments of
  run_softcal_waterbalance
- build_wb_softcal_input now replaces download_sft_files
  and modify_wb_parms
- Variable names wer updated to be consistent with run_verify