Worldwide roles

This adds the necessary plumbing to allow people to be linked with worldwide offices. This can be done in two ways:

1. Using the existing roles mechanism.
Top-level appointments for worldwide offices should be specified using roles and role appointments, as with organisations. New role types exist for: Ambassador; High Commisioner; Governor; and Deputy Head of Mission, and these roles can now be associated with worldwide offices.

2. Using worldwide office appointments
Any non-top-level staff should be specified under the new Worldwide offices "Appointments" tab. Here, people can be associated with an office, along with their job title, bypassing the need to create individual roles and role appointments for each person working at the many worldwide offices.