Delivery interface should expose receiver settlement mode

AMQP 1.0 permits the receiver settlement mode to be overridden for an individual transfer. This overrides the receiver settlement mode that was agreed at link establishment time for the scope of a single delivery only. See: http://docs.oasis-open.org/amqp/core/v1.0/os/amqp-core-transport-v1.0-os.html#type-transfer

The Proton (Engine) API does not currently expose this ability to the user. The Delivery interface should be augmented so that:

• as a user of Sender, I can override the receiver settlement mode for an outgoing Delivery.
• as a user of Receiver, I can determine the settlement mode in force an incoming Delivery.