Bump CKEditor to version 4.2.1

CKEditor 4.2.1 was just released: http://ckeditor.com/blog/CKEditor-4.2.1-Released

This update includes some critical fixes, particularly "Save toolbar button saves only the first editor instance."  That's the main reason for this pull request.

All I did here was replace /vendor/assets/javascripts/ckeditor with the "full package" download of CKEditor from http://ckeditor.com/download  If there is more to it than that, reject this pull request.  However, my installation of CKEditor appears to be working fine.

Thanks very much for working hard on this gem, it is awesome.