Layer name consistency

[rafaqz]

It seems fairly common that layer names as used in urls and filenames are not the same as the layer names listed on the web page where you download said files. This is the case for EarthEnv where e.g. shannon and others are lower case for some reason or other, but are listed as upper case, while half the layers are uppercase in both instances.

Datasets like ALWB take this to the extreme by using totally different layer names on the download page to what they use internally. BioClim uses bio_15 (WorldClim) or bio15 (CHELSA) but names are also displayed on the website as BIO15 (WorldClim) and Bio15 (CHELSA). We just use the number. But should probably allow all variants.

To avoid confusion we should allow both internal and listed layer names to be used. This essentially means defining a lookup Dict for each source that lists all the display names and technical names, and connects them to the technical names.