Bump ckeditor from 4.7.3 to 4.12.1 in /web-ui

Bumps [ckeditor](https://github.com/ckeditor/ckeditor-releases) from 4.7.3 to 4.12.1.
- [Release notes](https://github.com/ckeditor/ckeditor-releases/releases)
- [Changelog](https://github.com/ckeditor/ckeditor4-releases/blob/master/CHANGES.md)
- [Commits](https://github.com/ckeditor/ckeditor-releases/compare/4.7.3...4.12.1

)

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