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. 
Thinking about it a little more, I think the second query is difficult to wrap into the first without a subquery.  Don't care if we go with a subquery or with a separate query that depends on the first, but queries 1 and 2 can be combined in this way:
```sql
SELECT S.study_id, S.study_title, U.name as owner_name, U.email as owne
       S.metadata_complete, S.number_samples_collected, SP.name as pi_name,
       SP.email as pi_email, count(SRD.raw_data_id) as num_raw_data, SS.status,
       array_agg(PMID.pmid) as PMIDs
FROM qiita.study S
     JOIN qiita.study_status SS on S.study_status_id = SS.study_status_id
     JOIN qiita.study_raw_data SRD on S.study_id = SRD.study_id
     JOIN qiita.study_person SP on
        S.principal_investigator_id = SP.study_person_id
     JOIN qiita.qiita_user U on S.email = U.email
     JOIN qiita.study_pmid PMID on S.study_id = PMID.study_id
WHERE S.study_id = 10045
GROUP BY S.study_id, S.study_title, S.metadata_complete,
         S.number_samples_collected, SP.name, SP.email, SS.status,
         U.name, U.email;
```
This differs slightly from the earlier version because it has two additional columns in the group by (which i accidentally just left out of the first version, which was broken because of this), and adds the array_agg on distinct pmid