Add shared sponsors to relatedBills

[aih]

In data.json, the sponsor item is an object of the form:

cosponsors is an array of the form:

In relatedBills, if the two bills share the sponsor (both bioguide id and name), add the cosponsor item. If they share any sponsors, add a sponsors array with the shared sponsors (as they are found in the related bill).

[aih]

Working to show cosponsors that are shared. Note that not all data.json contains cosponsor data.