CSV columns should always be string-valued

[kerinin]

When loading two different portions of a CSV file, it's possible to create inconsistent DB schemas. I propose that we always treat CSV columns a strings.

[bjchambers]

This could make sense, but would likely have efficiency problems -- manipulating strings is far more costly than manipulating integers. An alternative would be to default to treating them as strings, but allow the user to specify a schema. And/or make it configurable with some options:

1. Use this schema ...
2. Default to strings
3. Default to inferred types