in proquest, use new mag fields at level 0

[f-hafner]

currently, we're selecting based on pq_fields_mag which are imputed in load_proquest/correspond_fieldofstudy.py. Now that we have the predicted MAG fields, we could use this for selecting on field level 0.

This query computes a table similar to pq_fields_mag:

create table pq_fields_mag_future as 
select goid, ParentFieldOfStudyId AS FieldOfStudyId, sum(score) as score  
from (
    select goid, fieldofstudyid, ParentFieldOfStudyId, score 
    from pq_magfos 
    -- join parents at level 0
    inner join (
        select childfieldofstudyid, ParentFieldOfStudyId
        from crosswalk_fields
        where parentlevel = 0
    ) as crosswalk 
    on (pq_magfos.fieldofstudyid = crosswalk.childfieldofstudyid)
)
group by goid, parentfieldofstudyid

It could replace pq_fields_mag if we use the rank by score to replace the column position in the current table.
It would break some things: setup_linking may need to be adjusted, as well as link/topic_similarity_functions.py