hrdemog: Add "Extended Demographics" extension

Create an extension, "org.civicrm.hrdemog". The extension defines a new custom data group called "Extended Demographics" with the following fields:

• Nationality ("Select" a country)
• Ethnicity ("Multi-Select" list)
• Religion ("Select" list)
• Sexual Orientation ("Select" list)

This should be a normal custom-data group (displayed "Inline" on the "Summary" tab), and all fields should be searchable.

To determine the options to put in the three lists, search the web to find if someone has published a good list that can be repurposed. At a minimum, the US Census Bureau should have a well-known list of options.

The extension should go in the "https://github.com/civicrm/civihr/" git repository following the same conventions as the other extensions.

(Note: I'm a little skeptical about collecting some of these fields in HR, but I'm not HR expert... we'll see what feedback it gets from test users...)