[TASK] Make the extension standalone

Classes/Backend/Ajax.php

Classes/Form/Element/LicenceStatus.php

Classes/Hooks/LicenceCheckHook.php

Configuration/Backend/AjaxRoutes.php

Configuration/FlexForms/flexform_sgyoutube_youtube.xml

Configuration/Services.yaml

README.md

Resources/Private/Layouts/Default.html

Resources/Private/Templates/Youtube/Index.html

Resources/Public/JavaScript/Backend/LicenseNotification.js

Resources/Public/JavaScript/Dist/main.bundled.min.js

...s/Public/JavaScript/Dist/sgYoutubeLightbox.bundled.min.js

Resources/Public/JavaScript/Modules/sgVideo.js

Resources/Public/JavaScript/Modules/sgVideoLightbox.js

Resources/Public/JavaScript/main.js

Resources/Public/Sass/Modules/_sg-video.scss

Resources/Public/StyleSheets/main.min.css

Resources/Public/Vendor/iframe-lightbox/.browserslistrc

Resources/Public/Vendor/iframe-lightbox/.editorconfig

Resources/Public/Vendor/iframe-lightbox/.eslintrc