Import as Person if first_name exists

Fixed bug: If first_name exists and company_name exists the importer
tried to create a Company, dropping the first_name. Error found when
multiple records with first name only and same company name created
naming collisions while creating multiple companies.
Importer reuses empty company records

When importing an imported person with an assigned company will create
that company. Later in the import process, we may run into the company
record itself.

This will find the existing record by name and check if it has any other
attributes (that it is mostly empty). If it does not, it will add the
additional attributes from the company record.

On the other hand, if an existing record has additional attributes
already (meaning it was imported before), we throw an error rather than
overwriting the existing attributes.
Added DC to US inference method

Missing DC from the US importer inference method. When records were
imported with DC as the state name, it failed.