Add support for LDAP groups in LdapUserMapper when redback is used for auth login to an application like Continuum

The Redback LDAP configurations used by other applications like Continuum, only allows for setting UserBaseDN as a selection criteria when authorizing access to the application.
In any case where all users are located in the same ldap tree/sub and all users should be granted access, this is fine.
But most of the time you would want to grant access to applications either by setting a special permission or attribute on users, or you would define an ldap group where authorized users are added.

The LdapUserMapper and the redback-common-ldap source should support both defining groups and/or user attributes as a filtering mechanism when access is granted.