Need to standardise `taxon_rank` values

[ehwenk]

@wcornwell @fontikar Two issues:

• we currently have a mix of lowercase and uppercase taxon_rank values
• we currently have a mix of English and Latin taxon_rank values

We should select a standard and implement it when the taxonomic resources are read in.

It seems that lowercase is the standard (DarwinCore, International Association of Plant Taxonomy, a style guide), but NSL uses uppercase:

• https://stylemanual.com.au/contents/subject-areas/biology/naming-organisms/general-principles-formal-taxonomic-names
• http://rs.tdwg.org/dwc/terms/taxonRank
• https://www.iapt-taxon.org/nomen/pages/main/art_3.html
• https://www.iapt-taxon.org/nomen/pages/main/art_4.html

Also, do we want the output values to be:

form, variety, subspecies, species, genus, family, class subclass

or

forma, varietas, subspecies, species, genus, familia, classis subclassis

Right now, the column headers are in English (e.g. genus, family, subclass), but the values in the taxon_rank column are Latin (Familia, Varietas, Forma)

[wcornwell]

english, DarwinCore