* Corrected bug in NHibernate mapping for UserOAuthProvider

Currently NHibernateUserAuthRepository tries to save and query based on the original UserOAuthProvider. This type contains a Dictionary<,>, which NHibernate can't use because it uses its own implementations (from Iesi.Collections) of generic interface types. I have therefore created UserOAuthProviderPersistenceDto which wraps UserOAuthProvider, and uses IDictionary<,> instead of Dictionary<,>