Add Biomappings support for the DKG

[cthoyt]

Closes #69. This PR does the following:

1. Adds relevant biomappings into the DKG
2. Adds a script for constructing a local Gilda cache based on the DKG
3. Adds a script for adding predicted lexical mappings to Biomappings from a subset of namespaces in the DKG (ones related to epi)
4. Improves RDF construction (remaps the new synonym predicates and the unqualified biomappings predicates to DeBiO terms)

This also updates code relevant for updates to the PyOBO and bioontologies

[codecov-commenter]

Codecov Report

Merging #95 (8fe2d81) into main (7f849c7) will not change coverage.
The diff coverage is n/a.

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[cthoyt]

@bgyori tested and ready!

[cthoyt]

We had several chats about this being ready, I just added a few minor updates for pyobo + bioontologies before merging