Add gettext strings

git-svn-id: https://plugins.svn.wordpress.org/simplr-registration-form/trunk@1053678 b8457f37-d9ea-0310-8a92-e5e31aec5664
Add first version of pot file and nl_NL

git-svn-id: https://plugins.svn.wordpress.org/simplr-registration-form/trunk@1053680 b8457f37-d9ea-0310-8a92-e5e31aec5664