created MetricsBucketAggregator that aligns the Metrics into buckets the length of the interval before aggregating
update cassandra url
move calculations to flush(); make Gauge report bucket boundary as timestamp; add tests
Merge branch 'master' of github.com:DataDog/dd-agent into statsd_buckets

Conflicts:
	.travis.yml
clean up pylint warnings
changed method of continuing empty counters; buckets are flushed with timestamp of the beginning of the bucket
dogstatd interval changed to 2 sec. separate aggregator interval (bucket size) from dogstatd interval (how often flush is called)
fix for intermittent test failure
update logging intervals
reduce amount of logging on flush
change log to warning
Merge pull request #824 from DataDog/statsd_buckets

Statsd buckets