Adding a where_valid country to Safetynet

from Al

 

I have updated the where valid in regulatory_body_to_text function check and it's ready to be merged into production. I created a where_valid list of values stored in constants/__init__.py file. Just add a new country code to the list to allow that country code and run the a2reload command in the terminal. If the where_valid value is not in the list, it will return N/a for the endorsedfor value.