Refactor ConsumeEventListener to simplify entity persistence

[gimikus]

Situation:
Now, ongr:import:full command pipeline's event listeners designed in way/paradigm what data is copied from source entity (document) to destination document. If onModify event listener do not creates document, onConsume event will skip this item.

Problem:
If you make some modifications to source entity it will be persisted only if document is set too (you override only persistDocument() method). If you need to persist only source entity from import item you have to override ConsumeEventListener setItem method, copy/paste method code and add entity persist after check what pipeline item is instance of correct class. ( https://github.com/ongr-io/ConnectionsBundle/blob/master/EventListener/AbstractImportConsumeEventListener.php#L108).
Solution could be:
It would be better just to implement persistence of entity if it is necessary.