Editing a field should notify FieldModifiedEvent

[cdw9]

https://github.com/plone/plone.schemaeditor/blob/master/plone/schemaeditor/browser/field/edit.py#L175

Currently editing a field notifies the SchemaModifiedEvent. But this doesn't pass the field information to a subscriber.

notify(FieldModifiedEvent(self.context.__parent__, self.field)) should be used here instead