Coordinate soil classifications

[pbuttigieg]

There are several systems out there, and they may be talking about the same soil using somewhat different criteria. To avoid representing the classification rather than the soil, we'll try to be conservative and use synonyms until there's good reason to believe the systems are referencing truly different entities.

I'm merging #331 #332 and #330 into this issue:

[pbuttigieg]

@celineaubert provided the following in the merged issues:

USDA orders of soil taxonomy are used in USA to classify soil.
Could you please add the 12 orders of soil taxonomy : Alfisol Andisol Aridisol Entisol Gelisol Histosol Inceptisol Mollisol Oxisol Spodosol Ultisol Vertisol. Definitions are here or here. COuld you also add the in-subset USDA order of soil taxonomy for these classes? Thanks.

Two of the FAO soil classes are not listed in ENVO: greyzem and podzoluvisol (different from podzol). link to the definition: [http://www.fao.org/fileadmin/user_upload/soils/docs/isricu_i9264_001.pdf]

The World Reference Base (WRB) is the international standard for soil classification system that replaced the FAO soil classification. The WBR soil groups are already in ENVO. Could you please add an in-subset World Reference Base soil groupfor the following soil groups: Acrisol Albeluvisol Alisol Andosol Anthrosol Arenosol Calcisol Cambisol Chernozem Cryosol Durisol Ferralsol Fluvisol Gleysol Gypsisol Histosol Kastanozem Leptosol Lixisol Luvisol Nitisol Phaeozem Planosol Plinthosol Podzol Regosol Solonchak Solonetz Stagnosol Technosol Umbrisol Vertisol?