Upgrade CKEditor to 4.11.2

CKEditor 4.11 has been released a while ago. The second patch release (4.11.2) is also available now. We should upgrade our fork, which is currently based on 4.9.2.

CKEditor 4.10 comes with various bugfixes, and some new plugins that could be handy for us:

• autocomplete (generic autocompletion feature)
• emoji (insert Emoji's easily)
• mentions (auto-complete user names)

CKEditor 4.11 has various improvements too:

• more fancy Emoji's with a dropdown
• the autolink plugin recognizes text that looks like a link and converts it into a hypertext link

Release notes can be found at https://ckeditor.com/blog/CKEditor-4.10-released/, https://ckeditor.com/blog/CKEditor-4.10.1-released/ , https://ckeditor.com/blog/CKEditor-4.11-with-emoji-dropdown-and-auto-link-on-typing-released/ and https://ckeditor.com/blog/CKEditor-4.11.2-released/ .