#14 application Metrics

Integrate Codahale's Metrics to the application.

### Reporting
- JMX managed beans
- Graphite if enabled in config.

### InstrumentedActors
- message receive counter
- message receive timer
- exception thrown rate

### TopicStatisticsActor
- use metrics to compute throughtput

### Per request Actor
- start meter
- timeout meter

### JVM metrics
- memory usage
- thread usage
- GC