Added storage lifecycle-events for save and delete. …

preSave / postSave
The only distinction between insert/delete is the absence of
$event->getId() (it's an empty string) in the preSave-event.

preDelete / postDelete
There is no $event->getContent() available, since a delete only requires
a contenttype and id.
Merge branch 'master' of https://github.com/bobdenotter/bolt