added in MongoIdentity and MongoIdentityEvidence classes.
changed credentials to support the new identity and evidence classes.
replaced MongoClientIdentity in Sasl code.
working through url builders and settings objects and tests.
changed Negotiate to Strongest, authType to authProtocol, and made admin the default database from connection strings.
removed MongoClientIdentity.
refactored authentication logic to be union of privileges.
cleaning up warnings.
removed all items related to credentials from MongoServer, MongoDatabase, and MongoDatabaseSettings.
removed copy of MongoConnection and some minor refactoring.