Add association for Manual and PublishTask

This commit adds an association marshaller between Manual and PublishTasks allowing us to make the most recent PublishTask available to the specialist-publisher frontend for feedback on how far the publishing task is from completion.

This association is read only!
Provide feedback of state of publishing manuals

Display a user centred message to notify the user of where the PublishTask is in the queue so that they are aware that when they press 'Publish' that there will be some time before the item is "published".
Assure errors are raised when recoverable errors occur