implemented Consumer Cancel Notifications

In case something happens to a queue (e.g. it is deleted) and we have consumers registered for this queue
the server will silently stop sending messages to the consumer while the connection is held open.
RabbitMQ implements an extension to AMQP-0.9.1 which allows the server to send a basic.cancel to the client in case it will stop sending messages for a particular consumer.

In my implementation php-amqplib will throw an exception if it receives a basic.cancel from the server.