Citationtrees

Creates network map from the database. Given a "root" doi or uri, creates edges from the root to citation groups, and from there to individual references in the group, so related references are linked through this intermediate node. Network nodes that correspond to references have short labels generated from titles, but titles aren't always included. 

In principle, the function should create a second level of citations, but I wasn't able to test this because the references in general didn't have their own reference information. Probably this is because there are few papers in the database?