Drawing form: Add Country of Origin field

What

Destination Unknown are interested in collecting the child artist's nationality, for the 'Drawings' interface of the DML Campaign Tool.

This should be presented as Country of Origin with a drop-down list of countries. See example here ('Origin' section) http://popstats.unhcr.org/en/asylum_seekers
This is another data field in a form that is already long and will add further time to fieldworker upload. The new field would sit below 'Age of artist' in the Details of artist section. Confirm with team whether we want to add this now. @EChesters @rocioleon @tanyapowell