Clean AliquotTube persistor.
Flowcell Persistor done. All specs pass.
Add ContainerPersistorTrait and use it for Flowcell.
DRYup plate and gel persistor.
skip container parent in parents_from_attributes.
DRY TubeRackPersistor up.
Add :deletable option to container persistor.

Decide if the contained class needs to be deleted or not.
Refactor Labellable Persistor. All specs pass.