fixed/refactored get_evaporation(): ignore empty hourly values for daily means
fixed get_evaporation(): ignore days, for which vpd/windspeed isn't available
added helper functions generate_daterange(), get_trial_daterange()
fixed get_soil_water(): retrieve trial dates from get_trial_dates()
- dates were extracted from evaporation data before (sometimes incomplete)
fixed #5: added culture ID to tsv output
workaround for issue #6: database/irrigation-without-control/stress
fixed values in all_trials.tsv
fixed culture ID handling in tsv output generation