Translate worldwide offices

This follows a very similar form to the translation for world locations, although
some of the admin interface is different.

It should be noted that to avoid application downtime this commit doesn't
remove *any* columns from the worldwide_offices table. Once the application is
deployed and restarted, the vestigial content columns on that table should be
removed, but not before.

https://www.pivotaltracker.com/story/show/44454707