Fix query by segment
* Changed topN queries to use joda Interval instead of string values
* topN by segment now implements BySegmentResultValue<Result<TopNResultValue>> instead of BySegmentResultValue<TopNResultValue>
* Added a unit test which failed uner the prior implementation.
Merge remote-tracking branch 'origin/master' into druid-845
Remove getIntervalString from BySegmentResultValue
Merge pull request #856 from metamx/druid-845

Fix query by segment