Doco updates and updated ckeditor

1. Doco updates for the usage of super.render when creating your own ``TextPlugin`` that contain children plugins.

2. CKEditor update contains security XSS patch and problems with 9998 family of issues with Chrome / Webkit. The 9998 issue includes WebKit inserting rogue <span> elements when editing. This is a huge issue that was fixed in the 4.4 series. Some 9998 family issues are outstanding, but the biggest ones are now fixed:

https://dev.ckeditor.com/ticket/9998

They can be seen the CKEditor change log under:

[Blink/WebKit] Fixed