Provide a fullPage property for message templates
In various parts of the UI, CiviCRM allows users to send a message template either on its own, or wrapped in a header and footer.
e.g. you can send a message template to a contact.
Or, you can create a mailing based on a message template, with additional header and footer.
CKEditor needs different settings at civicrm/admin/ckeditor?preset=civimail re: allowed HTML tags to support these two scenarios. With fullPage = true, the HTML is forcibly wrapped with html/head/body tags, and so a message template that includes its header and footer can be composed. With fullPage = false, html/head/body are silently stripped, so this is useful for message templates that should be used with a header and footer.
However, there is only one CKEditor setting for both of these scenarios.
I would propose a new database column where we can indicate if a message template is "fullPage" - i.e. includes header and footer, or not fullPage, i.e. designed to be used with header and footer.
This would allow us to toggle the fullPage setting appropriately. It would also allow us to prevent a user from sending a message template that needs a header and footer without one, or wrapping a message template that includes its header and footer with an additional header and footer.