Allow Serialization based on session attribute name in Redis

[rwinch]

This is a brain storm on how to handle https://github.com/spring-projects/spring-session/issues/348#issuecomment-181205839

For example, a org.springframework.core.convert.converter.Converter<Map<String,Object>,Map<byte[],byte[]>> could be used to prior to saving the delta. Then the we could provide a org.springframework.core.convert.converter.Converter<Map<byte[],byte[]>,Map<String,Object>> to convert back to the objects just after we load the data.

This would mean users could provide a mapping of session attribute name to the object rather than having to include class names in the serialization data.

[aterleto]

This could help solve - Issue#1330 RedisOperationsSessionRepository loadSession ClassCastException