Add Apps session metrics job
Uses Twitter's algebird to compute percentiles
Removed geometric mean computation (not doable)
This job runs for 1 day of data with 6 executors and
and 2g per executor in 6 minutes if after we filter data
we lower parallelization 1 order of magnitude to do computations.
Input to the job is an output directory where to persist the data
and a date. Job appends data to file.