kegg: add pathway-to-disease, pathway-pubs, gene ortholog classes
kegg: add pathway-to-disease, pathway-pubs, gene ortholog classes

* add pathway-to-disease, where the pathway is causally_upstream_or_within the disease_id (process to process relationship).  addresses #89
* add pub ids is_about pathway_id
* add equivalence mapping between the KEGG-path:map* ids and KEGG-path:ko* ids.
* add ortholog classes (these are special kegg-constructs, sortof like an ubergene, that we classify here as a DATA:gene_family).  partially addresses #141
* add pathway-to-gene-ortholog class.  we treat the KEGG-ko classes similar to genes, when they are added to pathways
* add human gene-to-kegg-ortholog mappings.
* add EC ids as xrefs to genes

monarch-initiative/dipper,monarch-initiative/dipper,TomConlin/dipper,monarch-initiative/dipper,TomConlin/dipper