PIM-1544 : Create abstract entity processor and make association processor class extending from abstract entity processor
PIM-1544 : Refactor Processors
PIM-1544 : Update CHANGELOG
PIM-1544 : Fix PHPCS
PIM-1544 : Update translation messages
PIM-1544 : Update translations for import
Merge pull request #473 from akeneo/PIM-1544

PIM-1544 : Refactoring ImportExport bundle