Delete from storage when deleted from Plone

[wengole]

Currently when content is deleted from Plone, it will remain in S3 as there is not Celery task to remove it.
Need to hook into the event fired by Plone and remove the content from S3 at time of deletion

[wengole]

This should also handle removing the file from S3 if a file attachment is changed to one that is smaller than the threshold and thus not uploaded. This causes a current bug where the old version will be served from S3 even if the attached file is replaced.