Support readOnly on openapi2 (swagger)

[DanielMerchan]

Currently we have migrated all our APIs from Blueprint to Swagger 2.0 (Open API 2.0).
We have seen readOnly on schema attributes is ignored and it makes confusing the rendering of the body requests for the POST, PUT or GET operations which uses the same Schema object.

In Swagger editor, the readOnly attributes are automatically hidden for POST, PUT, PATCH operations.
However, in Apiary you see the entire object always which can create confusion to consumers which attributes are really necessary or not.