Make all functions in 'graphql-server/utils/helper.js' work with internal IDs

[asishallab]

The helper module is located in the graphql-server skeleton project. At least one of the functions parseOrderCursor still expects the idAttribute of a data model to be literal id, i.e. our former default.

1. Identify all functions that require adjustment to work with custom internal ids.
2. Fix these functions, e.g. by accepting another argument idAttribute so that they know which attribute to query in the respective model.

Consider moving the whole helper module into the code-generator, which should only copy the module file into the respective skeleton project. If this helps circumnavigating such issues in the future, move the module into the skeleton project, otherwise leave it where it is.

Expected work load: 2 to 3 hours