Change BSONBinary UUID subtypes to match BSON spec

UuidSubtype points currently to BSONBinary subtype 0x03, but the BSON spec describes this as "UUID (Old)". So I renamed UuidSubtype to OldUuidSubtype (just as the "Binary (Old)" is named OldBinarySubtype. The BSON spec describes the "UUID" subtype as subtype 0x04. I added UuidSubtype again with the value 0x04.