WIP: optimization on displaying studies list

I got really tired of how slow is the studies display when having so many studies so I started working on https://github.com/biocore/qiita/issues/601. This is the initial optimization of /private/. I want to have some feedback before working on the others. 
The solution here was to absorb queries 2 and 3 into query 1 using [array_agg](http://www.postgresql.org/docs/8.4/static/functions-aggregate.html)