Fixing the Apprentice usage histogram.
Fixing the Apprentice usage histogram.

- Migrating to the new version of petl, which depracated rangeaggregate
  and rangecount.  Now we manually compute the bins, and it may be faster
  this way.
- Using the table output by the ETL step for the queries.  This moves us
  a step closer to proper data warehousing.

sideeffects/stats_houdini