Adds a dismissable message to the CMS object code editor indicating that the PHP code section of a CMS object cannot be edited when `cms.enableSafeMode` is `true` (or when debugging is disabled if `null`).
Credit to @mjauvin.
This is modeled after the Backend helper. Primarily used to generate URLs for the frontend, these are piped through the CmsController action. It would also be a good place to add a hook, if necessary later.
