Feature/490 json attributes as object

### Description
The rendering of ContextAttribute for JSON has now two possibilities:
1. As a vector (the old way)
2. As an object, with each attribute as an object inside

(1) is the default rendering method, while the second method is achieved adding the URL parameter

    attributesFormat=object

Fixes issue #490.
> Attributes with same name and types.

I meant "Attributes with same name and types without ID" (I see the case with A3-test in step 5, but it uses ID).

I think is would be easy to include: it is just a matter of "copy-paste" repeat 3-5, removing the ID stuff.