Add 'phone home' functionality that allows a da.live admin to refresh all client editors

In some cases we need to refresh the da.live client-side code more or less immediately on demand from an administrator.
This could be needed when there is an urgent fix to be rolled out, or when the protocol between da-live and da-collab or da-admin changes.

For the fix to https://github.com/adobe/da-live/issues/378 we would need such functionality, because the protocol between da-collab and da-live changes.

Adding a 'phone home' periodic check to the editor may be a way to do this, but there might also be another way.

Start by reviewing the da.live client-side editor and how it communicates with da-collab and da-admin. Determine how an administrator could request an immediate refresh and define the behavior needed when the da-collab or da-live protocol changes. Done means all client editors can be refreshed on demand through an agreed mechanism.

Written by the indexing model from the issue text.