[doc] cssref.html copyright is incorrect

Jasper says:

"The basic requirement is to add to Gradle build a task to copy CSS doc in Ensemble sample under a BSD license. Needs to be a copy task in Gradle as doc is changing and don't want two out of sync copies. Also the standard docs copyright footer will need to be replaced with a BSD one. The idea think would be to convert it to XML from HTML as well to make it better readable by tools and IDEs like the eclipse plugin.

Tom Schindl has been asking for this for a while as it prevents efxEclipse being included in eclipse distro. The can not accept the license of the CSS ref doc. Tom already has code to convert HTML to XML so maybe he could donate that."

Is sounds as if we want to make the CSS doc available under a BSD license (not sure about the Ensemble bit).