Add client scope role mappings

[carillonator]

Add functions to get/add/delete Client Scope role mappings. Note there are already unfortunately-named get/assign/delete_client_roles_to_client_scope functions, which act on a Client's "dedicated" scope. I am open to adjusting the naming here, the keycloak terminology itself is confusing. My new names do not help the confusion, but are more accurate. I've improved the documentation on the existing ones, and cross-referenced the others to avoid confusing people.