Update CensusColumnNationality.php

[manf0001]

Hello, I would like to update the CensusColumnNationality.php to add more countries to it. Before I do, I was wondering if there are somethings I should know, or requirements that the original author had in mind.

Also I noticed that it has listed England, Scotland and Wales as British for the Nationality. I know Wales, and Scotland are part of the United Kingdom, but wouldn't the nationality, be Scottish, and Welsh respectively? But if I'm wrong, I'll leave it be.

Thank you.