Carriage return in body tag in CKEditor.ContentSheet breaks realtime with some browsers

Starting with Chrome 60, the carriage return in the class field of the body tag in CKEditor.ContentSheet seems to generate a browser fight with at least Chrome 59. This Generates sync errors.

Possible fix: fix CKEditor.ContentSheet as this is invalid HTML
Fix if we want to work with older CKEditor XWiki integration: fix this carriage return before doing sync..

This bug might not require RTWysiwyg fix but it's there to know this problem can happen and means incompatibility with current CkEditor (1.16) integration and Chrome 60.