Issue #1950098 by Wim Leers: Update CKEditor library to 4.1.

core/misc/ckeditor/CHANGES.md

core/misc/ckeditor/ckeditor.js

core/misc/ckeditor/plugins/a11yhelp/dialogs/lang/km.js

core/misc/ckeditor/plugins/a11yhelp/dialogs/lang/th.js

core/misc/ckeditor/plugins/image/dialogs/image.js

...isc/ckeditor/plugins/sourcedialog/dialogs/sourcedialog.js

core/misc/ckeditor/plugins/specialchar/dialogs/lang/pl.js

core/misc/ckeditor/plugins/specialchar/dialogs/lang/th.js

core/modules/ckeditor/ckeditor.module