Use external primary keys for Rangers

[wsanchez]

Right now, we reference Rangers by handle in IMS. If you change you handle in the Clubhouse, IMS will lose these references, so we should remember both.

I think we need to keep using handles in the JSON API, and that should be fine, but the database should add a RANGER table which indexes the handles by the external primary key.

In the current MySQL database, that primary key is an int. But in a text file, the primary key might be the handle, or a GUID. So I think we should store the key as text and convert in the client.