Misleading NPV input

A quick test adding `readydates` for all the wells in the input to `fm_npv` suggested that the well cost for wells without the `readydate` is silently ignored. Not sure if it is ideal behavior, I vaguely remember `fm_npv` job complaining about missing dates in the past but I might remember it wrong. This is confusing in the tutorial since the well cost is specified in the input file to NPV for all the wells. This affects current well rate tutorial. For that adding `readydate` for all the wells should solve this.