Add Kryo serializer for java.util.Optional

[alexbudarov]

Description of the bug or enhancement

Optional in Java 8 is not serializable. It makes inconvenient to use it in CUBA applications, because Optional can't be a result of a middleware service method. And middleware services are an essential internal part of CUBA application.

But for those people who use Kryo serialization - it is easy (and safe?) to make Optional kryo-serializable.

[jreznot]

Isn't it a trap that somehow Optional will be Serializable in cuba only with Kryo? Do you want to stick with only one serialization option?

[alexbudarov]

Choosing serialization implementation is not an option for us. Kryo is just so much better that there is no choice for us (who use remote thick client).

[jreznot]

Is it OK if we just provide you options to enable this behavior ?

[alexbudarov]

Well, we already can subclass KryoSerialization and register the serializer ourselve if we want.