This is a function that invokes the PANTHER.db Bioconductor library to extract a list of pathway mappings
to be used in gene set enrichment tests. Specifically, the function returns a named list of pathways, where each element contains
Entrez IDs. Users should not generally call this function directly as it is invoked internally by the higher-level
The species of the cells used in the screen. Currently only 'human' or 'mouse' are supported.
A named list of pathways from
Russell Bainer, Steve Lianoglou.