Limit the number of exported databases to keep

The task "Admin - Export databases for backup" exports a copy of the database to a location on disk. Executing this task many times may result in disk being eaten up. I suggest a setting that limits the number of kept exports such that once reached, the oldest export file will be deleted prior to performing the export and creating a new file. This would limit the disk usage as well as aid in the overall cleanliness of the export directory.