EcoMap should parse eco.owl as ontology

[dustine32]

To move away from relying on gaf-eco-mapping.txt and gaf-eco-mapping-derived.txt we should fetch and parse eco.owl into an Ontology. With the whole ontology, we can compute closures for ECO codes indirectly mapped to a GAF evidence code (e.g. IDA) as well as access GO_REF references for terms (via oboInOwl:hasDbXref).

Example: if evidence type ECO:0001162 in a GoAssociation is being written out to a GAF line, this hierarchy should connect it to IDA as the evidence output value:

ECO:0001162 -> ECO:0000314 -> IDA

Tagging @kltm @cmungall

[dustine32]

evidenceontology/evidenceontology#289 (comment)