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. 
I think overall, the number of subqueries and sub-subqueries is confusing, and I would prefer to have this execute as 2-3 separate queries (this will still be a huge improvement over the 10-15 queries per study we are doing currently).  Also, joining with the ampersand (&) character seems unnecessary, since those are going to have to be split on ampersand later, so it would be better just to select those columns directly without joining them.