[Data Mapper] Visibility can't be defined

[janihur]

Description:

For any non-trivial application I'd prefer encapsulating the data mapping functions and records to their own namespaces (i.e. modules).

The Data Mapper doesn't support setting the visibility but that has to be added later in the textual representation.

Describe your solution(s)

One idea is to add an option in the similar fashion than there already is Make Separate Record Definitions when importing records from sample JSON.