Rewriting company_metrics.q for performance (and accuracy?)

Test Plan:
1. Started my own hive cluster, copy+pasted company_metrics.q into hive to execute
2. `select * company_metrics_new;` produces:

2012-04 200455  234261  110996
2012-05 157416  232637  104437
2012-06 153805  169153  83004
2012-07 126050  145249  77356
2012-08 242957  148085  81290
2012-09 519804  215446  162041
2012-10 418853  326151  193460
2012-11 247161  348870  156883
2012-12 199803  329898  132050
2013-01 299278  376685  165444
2013-02 239556  356060  138591
2013-03 240054  369366  140862
2013-04 372975  406869  153169
2013-05 167038  243144  47856

Which feels right in the scheme of our webiste, but are drastically different numbers than what is currently in `select * from company_metrics;`

I have not run the old company_metrics.q script since Jace said it would take forever to complete, so my theories on the differences in output are 1) the company_metrics table is out-of-date, 2) my query is wrong, or 3) the existing query is wrong (due to the `count(distinct user)`?)

So, I need to figure out why there is a discrepancy, but wanted to get a few more eyeballs on this in case I am doing something dumb.

Next Steps:
1. Change the dashboard code to understand the new schema (are there any other callers that would need to be changed?)
2. Run the query over all-time to populate company_metrics

Reviewers: jace

CC: stephanie

Differential Revision: http://phabricator.khanacademy.org/D2329