Add further options to `galah_select()`

[mjwestgate]

At present there are two use cases for galah_select() that are not supported:

• option to deliver all fields (group = "all"?)
• option to deliver the default fields for that atlas (group = "default"?) i.e. the same as from the biocache

[mjwestgate]

• decision not to add group = "all"
• add group = "taxonomy" to get higher taxonomic columns

[daxkellie]

Implemented in version 2.0.2