Downloader exclusion approach may be too coarse

[james-skelton]

nedrexdb/nedrexdb/downloaders/__init__.py

Line 50 in 115573c

"drugbank",

At present, there's an exclusion for downloaders at the database level rather than file level. For example, at present, we state that the default downloader shouldn't be used for BioGRID and DrugBank. However, within a single data source, there may be some files that we don't need the custom downloader for and other that we don't.