Added "uuid" field to UserService so we set our own global unique
identifier for this service.
This will be used by uds actor
There is another field, unique_id, that is provided by ServiceProviders,
and that we do not control in any way it's format. This is used, for
example, by actor to locate it's own "uuid"
Adding UUIDs to several models that must have it
Finished adding uuid to models where they are convenient.
Next step is adapt REST api to use this uuids instead of "ids", and fix
code were ids are used to use new uuids
Migrating "basic" ids from db (that was autoincrements on mysql) to uuid
based requests