Add structure function linkage database data

consider curated enzyme structure function relationships from the structure function linkage database. For example: http://sfld.rbvi.ucsf.edu/django/superfamily/1/

would need to pull in enzyme reaction functions into the import chain.
description of downloads is here:
http://sfld.rbvi.ucsf.edu/django/web/networks/

We should discuss what might be most relevant to pull.
Note also their similarity assignments.

reactions are here: http://sfld.rbvi.ucsf.edu/django/reactions/