Add support of polymorphic types

[artem-v]

Subj.

Consider to write header _type conditionally to the response message. For example it's possible to deduct that class in return type (or in @Response annotation) is abstract or interface and store this polymorphic indicator (e.g. boolean morph flag) in the MethodInfo.

[segabriel]

IMHO we should delete this header (_type) at all.

[eutkin]

Could it allow a user to add custom codecs (which would take precedence over the default codec) for some complex cases?

[eutkin]

I learned that we can only have one argument in the service interfaces. What if we wrap all interface arguments in an array and pass an array of types or other information to decode?

[artem-v]

@eutkin
see comment #639 (comment)

[artem-v]

It's agreed it can be solved on encoder/decoder level. Closing.