Add support for XEP-0184: Message Delivery Receipts
Description
Sometimes messages can be dropped if TCP connection with a client is broken (xmpp server can't always notice this). Smack already has support for this, so Spark needs an interface to use this.
Sometimes messages can be dropped if TCP connection with a client is broken (xmpp server can't always notice this). Smack already has support for this, so Spark needs an interface to use this.