Add an option to enable/disable exporters for entity, config and locale, and...

Add an option to enable/disable exporters for entity, config and locale, and make them disabled by default.

Entity and config exporters need to be explicitly configured to indicate what entities/config should be exported. That's not the case with locale exporter, which cannot be disabled and always exports data for all languages.

This is not a critical problem, since exporting locales is a trivial process that takes only milliseconds, but introduces several problems. The main one is that we can not check if an Output Formatter is already present, leading to errors by that automatic export process taking place.

Hence, we should add a "enable"/"disable" option in the list of exporters available in each "Settings for exportable entities | configurations | locales".