Import Script: add option to not use bulk import

[nichtich]

The import script uses bulk import so record that cannot be imported are silently ignored. Add an option such as --individual to import records one by one and emit errors. Result should be the similar to iterating over records and calling

curl -H "Content-Type: application/json" -d@record.json -X POST http://localhost:3000/data

for each record but the latter requires write endpoint to be enabled.

[stefandesu]

We could also import records one by one by default and add a flag --bulk to do bulk import. This might be more like what you'd expect if you used the import script.