CKEditor cache-busting timestamp value should use the web application hash

CKEditor uses a 'timestamp' property for a query parameter in all its requests that acts as a cache-buster. Currently, that timestamp value is a static random value that's generated every time the CMS boots. That means that just stopping and starting the CMS again will cause all users to re-fetch the CKEditor sources.

This can be improved by using the web application hash instead, which only changes when the hash of all JAR files changes.