Add missing return value from hooks.
Merge pull request #31 from leftclickben/RelationshipGeneratorPluginReturnFromHookMethods

Add missing return value from hooks.
Change structure of title generator plugin.

+ Use bundle hooks instead of label hooks, this enables modification of labels
  even when the user isn't adding or editing a label.
+ Labels are being removed and then re-added as editLabel() does not seem to
  work as expected.
Remove error_log() accidentally committed.