Merge branch 'feature_5168-unifyRootPageSelector' into 'master'

Classes/Command/SendMailCommandController.php

Classes/Controller/AbstractController.php

Classes/Controller/ConfigurationController.php

Classes/Controller/LayoutController.php

Classes/Controller/NewsletterController.php

Classes/Controller/QueueController.php

Classes/Controller/SiteController.php

Classes/Domain/Model/FrontendUserGroup.php

Classes/Domain/Model/Layout.php

Classes/Domain/Model/Mail.php

Classes/Domain/Repository/AbstractRepository.php

Classes/Domain/Repository/FrontendUserGroupRepository.php

Classes/Domain/Repository/LayoutRepository.php

Classes/Domain/Repository/MailRepository.php

Classes/Domain/Repository/TemplateRepository.php

Classes/Events/BeforeSendingFormsMailEvent.php

Classes/Exceptions/TemplateNotFoundException.php

Classes/Pagination/Pagination.php

Classes/Service/BackendService.php

Classes/Service/PlaintextService.php