move permission changing from -item to -worker

move permission changing from -item to -worker

The worker is the part closest to the methods, which will call the item
methods according to what it gets back from the methods, it is therefore
a better place to change permissions as it is very central and can do it
now at the point the item is assigned to a method rather than then it is
queued for download (and as before while dequeued via Done/Failure).

Git-Dch: Ignore