More partitioners

This introduces more partitioning options: daily, hourly and whatevery.
Also upgrades Joda-time 1.6 to 1.6.2.
To be considered: remove DefaultPartitioner.
If you use DailyPartitioner, do you still plan to use Sweeper?  DailyPartitioner would generate lots of small files in the daily/ folder (if each run is only a few minutes), but the customer probably would be fine with those small files if they chose the DailyPartitoner in the first place.