Expose the localize attribute

Localize attribute is currently hardcoded in nuxeo-directory-suggestion (https://github.com/nuxeo/nuxeo-ui-elements/blob/master/widgets/nuxeo-directory-suggestion.html#L218).

We should expose the attribute in nuxeo-directory-suggestion and mimic the behavior as described in JSF widget reference (http://showcase.nuxeo.com/nuxeo/layoutDemo/suggest_one_directory_multiple_widget/reference), to lookup for values in messages-*.json file.