Configuration change event for blog importer module triggers warning message

This issue was hidden by ESSENTIALS-711.

When a change to the blog importer configuration is successfully saved to the repository, the associated event handler takes (un)scheduling actions which trigger another save to the repository. Jackrabbit treats this as a potential infinite recursion and issues a warning: from within this "notification thread", no saves should be done.

There should be no warning when updating the configuration. Solution is to do the (un)scheduling from a separate thread.