Added support for order by Modified Date

git-svn-id: https://plugins.svn.wordpress.org/flexible-posts-widget/trunk@1016175 b8457f37-d9ea-0310-8a92-e5e31aec5664
Generated an updated POT file for translators.

git-svn-id: https://plugins.svn.wordpress.org/flexible-posts-widget/trunk@1016177 b8457f37-d9ea-0310-8a92-e5e31aec5664