Due to issue #17468, it is currently not possible to import big CSV formatted subscriptions list.

This must in the end be fixed using eZScriptMonitor, but for the first release, a CLI PHP script should be provided, re-using the code the module already executes.

The CSV import web interface should be added a note explaining that big files aren't supported, and that the CLI script should be used instead, or the files split to ~1000 lines chunks.