Add ECOTOX Knowledgebase

[cthoyt]

I came across the ECOTOX Knowledgebase in https://arxiv.org/pdf/2112.04605.pdf. It seems to be centered around the ecological effects of chemicals (e.g., on certain organisms). This needs a bit more investigation to confirm is in scope for INDRA, and might be useful to come back to later

Homepage: https://cfpub.epa.gov/ecotox/
Direct download: https://gaftp.epa.gov/ecotox/ecotox_ascii_09_15_2021.zip
Information about file format: https://cfpub.epa.gov/ecotox/help.cfm?sub=term-appendix