Each GAF line should have a unique and deterministic URI

[dougli1sqrd]

A gaf file should produce a graph URI based on the group name.
So for Gaf group 'goa' and dataset 'chicken_complex', produce a URI http://www.ebi.ac.uk/GOA/chicken_complex/.

For a GAF line, we can produce a unique id with a hash function on that line, after any "piped" columns are sorted (alphanumerically?). Then for an instance of a term in a column of the gaf line, we use the id of the final identifier: {graphUri}/{lineHash}/{termId}.
For example, for goa chicken_complex:
http://www.ebi.ac.uk/GOA/chicken_complex/123abc/GO:0016021