move write_attribute and as_json patches to GlobalizeHelpers module so that Link gets them, and test module in isolation, + test methods on each translated attribute at model level with shared examples.
add url method to link backbone model so that we can update links directly, rather than through a collection.
patch serializable_hash rather than as_json in globalize helpers to ensure that translated attributes are included in json for associated models, and check with unit spec and integration test.
rename features to use 'link' instead of 'neta'.
rename json to hash in serializable_hash.