Fixes and enhancements for backend

[einorler]

Made fixes and enhancements for the backend part of the bundle:

• removed unused use statements
• renamed the methods in managers
• reintroduced translation id formation to overcome import issues
• reintroduced event listener for adding history on updated messages
• changed the process of importing translations from persisting with es manager to bulk
• enabled setting any es manager for translations (used to be only default)
• added getMessageByLocale method in Translation