Improve installation instructions in README
Add option to change user's digest settings when registering.
Add version_option to the workflow

This is so that the administrator can define which versions will trigger
the adding of the defined notification subtrees.

Without this fix, all edits of user objects will trigger the adding
of notifications. You probably only want the creation of new objects
(e.g. through registration) to do this.
Add content/move/after trigger type
Backwards compatibility for eZ Publish version 4
Don't add notifications if they already exist
Update README
Fix bug parsing DigestSettings