Consider explicitly setting title, the creator and the author of WebPreferences documents

Currently, WebPreferences are sent to the filter without setting any creator / author.

It's likely that they get imported as whoever is running the import, which is not very clean. We should probably set WebPreferences as the same creator/author as the corresponding WebHome document.

The title should also probably be set to $services.localization.render('admin.preferences.title') (but see https://forum.xwiki.org/t/drop-the-maven-xar-plugin-requirement-for-setting-the-title-for-webpreferences-pages/17515)