Keep the list of approvers synchronized between pages and opened change requests

When using explicit list of approvers, new change requests gets automatically a copy of the list of approvers coming from the page that has been edited. However, if the list of approvers of the page evolves, the list of approvers of the opened change request currently doesn't change. There is a need to ensure that those lists evolves too, but we need to ensure that it's still possible to edit individually the list of approvers on change request.

So I propose the following mechanism:

• we use a flag to determine if a change request list of approvers have been manually edited
• when the list of approvers of a document evolves, we automatically synchronize the list of approvers of all opened change requests, if their list doesn't have been manually edited