[WIP][TASK] NL-3241 Add base model relations

.gitignore

Classes/Domain/Model/Menu.php

Classes/Domain/Model/MenuGroup.php

Classes/Domain/Model/MenuItem.php

Classes/Domain/Model/MenuItemContent.php

Classes/Domain/Model/MenuItemLink.php

Classes/Domain/Model/MenuItemPage.php

Classes/Domain/Repository/MenuGroupRepository.php

Classes/Domain/Repository/MenuItemRepository.php

Classes/Domain/Repository/MenuRepository.php

Configuration/Extbase/Persistence/Classes.php

Configuration/ExtensionBuilder/settings.yaml

Configuration/TCA/tx_nlmenubuilder_domain_model_content.php

Configuration/TCA/tx_nlmenubuilder_domain_model_link.php

Configuration/TCA/tx_nlmenubuilder_domain_model_menu.php

...iguration/TCA/tx_nlmenubuilder_domain_model_menugroup.php

Configuration/TCA/tx_nlmenubuilder_domain_model_menuitem.php

Configuration/TCA/tx_nlmenubuilder_domain_model_page.php

Configuration/TCA/tx_nlmenubuilder_domain_model_submenu.php

ExtensionBuilder.json