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 do not think is confusing, I consider it expert querying, but perhaps
it's something worth discussing. Agree on & but this was the easiest way to
retrieve 2 columns (name/email) from another table without having to create
2 subqueries (which will be more expensive). Note that the split is already
implemented and is not terrible.