replace datasets: even more custom hacking because replace is hard
silent unhelpful pipe error traceback
load-datasets: use starting line number and count lines starting from 1
load-datasets: preserve validation_override for now
replace datasets: make sure date fields are present
replace datasets: allow date validation to fail in package_create
load-datasets: show average time of load of last (windowsize) datasets
load-datasets: output validation errors as json, not repr()