Lists does not supports aggregators.
The export manager will filter the aggregators applying on the export
depending on the interface implemented by the export: if the export implements
`Export\ListInterface`, no aggregators will be returned for this export.
- add a test for 'generate' ;
- the ExportType declare keys, and those keys are used in ExportManager;
- the export interface does not require the "has form" function, and
export form is taken into account