Unifying the channel and transport layers to use different data types

For Add, Modify and Delete operations, we have different data types of InstanceInfo, Delta and InstanceIdentifier (wrapper around the String id). Unifying these so that the transport layer can handle them.
I agree that this is a bit abstract right now, but the operational model is very much improved. We can iterate over this implementation later.  I would merge this change, unless you have immediate idea how to improve it further.