retroactively reward theme reviewer points for old theme revs (bug 909985)

We introduced theme review points for theme reviewers. But we only started awarding points for theme reviews after the 8.27.2013 push.

We have theme review logs since ~4.20.13, 8805 of them. This patch gives those theme reviewers their due and awards points for those 9000 reviews.

This is done through a migration. I tried to build it safe such that even if it is run multiple times, the DB state only changes on the first run (integrity). It also adds a note on the created ReviewerScore objects, marking them as manual and "RETROACTIVE".

![img](http://collegecandy.files.wordpress.com/2013/03/make-it-rain-guys.gif)