Issue #3171952 by Spokje, asishsajeev: Update CKEditor to version 4.15.0

core/assets/vendor/ckeditor/CHANGES.md

core/assets/vendor/ckeditor/ckeditor.js

core/assets/vendor/ckeditor/lang/cs.js

core/assets/vendor/ckeditor/lang/hr.js

core/assets/vendor/ckeditor/lang/it.js

core/assets/vendor/ckeditor/lang/nb.js

core/assets/vendor/ckeditor/lang/ru.js

core/assets/vendor/ckeditor/lang/sk.js

core/assets/vendor/ckeditor/lang/sv.js

core/assets/vendor/ckeditor/lang/ug.js

core/assets/vendor/ckeditor/skins/moono-lisa/editor.css

.../assets/vendor/ckeditor/skins/moono-lisa/editor_gecko.css

core/assets/vendor/ckeditor/skins/moono-lisa/editor_ie.css

core/assets/vendor/ckeditor/skins/moono-lisa/editor_ie8.css

...sets/vendor/ckeditor/skins/moono-lisa/editor_iequirks.css

core/core.libraries.yml