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. 
Would you mind adding a case for "sandboxed" to the if/elif/else block above (lines 67-74)?  I can foresee this causing bugs (i.e., raising `IncompetentQiitaDeveloperError` errors) if someone is using this function inside a `for` loop that is iterating over study types and statuses, and one of the statuses is `"sandboxed"`