Use gaf-eco-mapping-derived.txt in EcoMap in GpadParser and GafWriter

[dustine32]

Continuing on the work done in #620:

• [x] In GpadParser, ECO codes that are indirectly mapped to a GAF code via an ECO ancestor should be allowed.
• [x] In GafWriter, these ECO codes should be converted to their indirectly-mapped GAF codes.

To do this we will use the gaf-eco-mapping-derived.txt file in EcoMap as needed:

• The GpadParser will default to checking for ECO->GAF code mappings in the derived file.
• The GafWriter will first check the non-derived gaf-eco-mapping.txt for mapping. If none present, it will fall back to the derived file.

[kltm]

@dustine32 Great! Merged https://github.com/biolink/ontobio/pull/625

[dustine32]

Tested in GO pipeline snapshot and release and confirmed this works as intended.