Add metrics

The latest refactor dropped a bunch of metrics. We need to re-add them.

Classes that need metrics:

• Add metrics to SamzaContainer/SamzaContainerMetrics
• Add metrics to TaskInstance/TaskInstanceMetrics
• Add metrics to TaskStorageManager
• Add metrics to MessageChooser
• Add metrics to DefaultChooser
• Add metrics to SystemConsumers
• Add metrics to SystemProducers
• Add metrics to KafkaSystemProducer
• Add metrics to KafkaSystemConsumer
• Add metrics to BrokerProxy
• Add metrics to CachedStore
• Add metrics to LoggedStore
• Add metrics to KeyValueStorageEngine
• Add metrics to LevelDbKeyValueStore

We definitely need msgs/sec, bytes/sec at both the container and task level. We also need reads/sec writes/sec on the stores. A lot more, as well.