Disabled Payson Sandbox setting, enabled live transaction server

git-svn-id: https://plugins.svn.wordpress.org/simple-payson-payment/trunk@999044 b8457f37-d9ea-0310-8a92-e5e31aec5664
Adjusted readme

git-svn-id: https://plugins.svn.wordpress.org/simple-payson-payment/trunk@999048 b8457f37-d9ea-0310-8a92-e5e31aec5664