[cms] Remove empty folder structure in CKEditor [5.2.2-B2]

In-Portal uses CKEditor as it's WYSIWYG editor. Over time we've upgraded it several times and since CKEditor developers just love to move folders around and delete them we'll ended up in lots of empty folder structures (e.g. deleted CKEditor plugins) while importing these changes into Subversion repository. 

Solution

Plan:

1. create migration script (can be saved in "/tools/" to be reused later) that will delete empty folders. If a folder is detected, that only contains empty folders, then instead deleting them delete that (parent) folder.
2. run script on the "/core/ckeditor/" folder
3. commit the changes

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