Updated support for Austrian Atlas (#126)

[mjwestgate]

• add extra API links for Austrian atlas, check all supported functions work
• add new function R/show_all_atlases.R/species_facets to ensure correct field is used to define unique species in different atlases
• update test-international.R to ensure all supported functions for a given atlas are tested.
• bug fixes to show_all_reasons and show_all_fields
• search_all now supports a taxa argument