GDS::SSO::User has a disabled field

www.agileplannerapp.com/boards/173808/cards/5886

This field represents a user's Signon state, so that
apps can decide how to treat them differently. For
example, Signon can set `disabled` to true for
suspended users.
Merge pull request #62 from alphagov/gds-sso-user-should-reflect-signon-suspension-state

GDS::SSO::User has a disabled field