ILSGateway product stock migration and first reports

@czue PR contains migration of some small part of stock data from ILSGateway. Some logic is directly moved from ILS.
This `if` is a little messy

```
        headers = []
        rows = []
        if not self.needs_filters and data_provider.show_table:
            headers = data_provider.headers
            rows = data_provider.rows
```