Reinstate $types parameter for back-compat with 1.0

$types is only necessary in `get_taxonomies` and `add_taxonomy_data`;
however, we need to leave it in the argumentss list for ALL methods in
order to avoid breaking any plugins built to interoperate with v1.0.

get_taxonomy (singular), prepare_taxonomy, get_terms, get_term,
and prepare_term should all have their $type parameter removed in 2.0.