Creating service keys and setup wizard helpers

• Let you supply your own URL for discovery documents in gar_discovery_api()
• Change defaults on gar_create_package() to check = FALSE, github=FALSE
• Add class 'list' to gar_discovery_*() objects so they work with jsonlite
• Add gar_service_list() and gar_service_get()
• If using gar_service_create() and it already exists, will return existing via gar_service_get()
• Move the setup wizard functions from googleCloudRunner to googleAuthR so they are available for all packages.
• Remove deprecated new_user param from gar_auth()