Replaced deprecated attribute_escape function with esc_attr

git-svn-id: https://plugins.svn.wordpress.org/postman-widget/trunk@1030000 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fixed undefined index warning in options page

git-svn-id: https://plugins.svn.wordpress.org/postman-widget/trunk@1030002 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated add_options_page call

git-svn-id: https://plugins.svn.wordpress.org/postman-widget/trunk@1030004 b8457f37-d9ea-0310-8a92-e5e31aec5664