Kafka spout can't show acks/fails and complete latency when auto commit is enabled

The storm-kafka-client spout currently emits tuples with no message ids if auto commit is enabled. This causes the ack/fail/complete latency counters in Storm UI to be 0. In some cases this is desirable because the user may not care, and doesn't want the overhead of Storm tracking tuples. avermeerbergen expressed a desire to be able to use auto commit without these counters being disabled, presumably to monitor topology performance.

We should add a toggle that allows users to enable/disable tuple anchoring in the auto commit case.