Specify datetime fields are datetime columns in schema

First step in supporting datetime in fields that are datetime.
Specify *_at system columns are datetime
Rename improperly named test variables
Refactor shared record data

Separate good record data for use in some specs.
Piggy back bad record data on top of this, for reuse.
Parse datetimes from *_at fields in record data

This parses datetimes from system columns in the record data.
These fields aren’t ever touched by an extractor, so we needed to do
some processing on them on their own.
Parse datetimes from DateTime fields in record form values

When working with a DateTime field value, parse it, so it can be
inserted into fusion tables in the proper format.