Missing R classes for imported objects

[TanguyBarthelemy]

Comparing versions 2 and 3, the functions used to import workspaces don't create the same structure in R. In version 2, after the reading from the java object, a R object with a class is created.

It's the class "workspace" for the ws object:

https://github.com/jdemetra/rjdemetra/blob/3b8fcbdc6e8dfee840373a1911ba07da8f32963a/R/import_workspace.R#L42

It's the class "multiprocessing" for the mp object:

https://github.com/jdemetra/rjdemetra/blob/3b8fcbdc6e8dfee840373a1911ba07da8f32963a/R/import_workspace.R#L82

It's the class "sa_item" for the SaItem object:

https://github.com/jdemetra/rjdemetra/blob/3b8fcbdc6e8dfee840373a1911ba07da8f32963a/R/import_workspace.R#L88

In v3 none of this three objects gets a class at it is imported in R.

Should we add classes?

[annasmyk]

yes we should for clarity and further manipulation's sake