terms_updated_messages filter

[johnbillion]

In the same vein as #18710 we should add a terms_updated_messages filter for the term management screen. Messages are currently hardcoded as 'Item added', 'Items deleted', etc.

Patch which introduces a term_updates_messages filter.

Plugin usage:

function term_updated_messages( $messages ) {
	$messages['foo'] = array(
		0 => '',
		1 => __('Foo added.','foo'),
		2 => __('Foo deleted.','foo'),
		3 => __('Foo updated.','foo'),
		4 => __('Foo not added.','foo'),
		5 => __('Foo not updated.','foo'),
		6 => __('Foos deleted.','foo')
	);
	return $messages;
}
add_filter( 'term_updated_messages', 'foo_updated_messages' );