Added support for hidden fields.

git-svn-id: https://plugins.svn.wordpress.org/wpgform/trunk@801500 b8457f37-d9ea-0310-8a92-e5e31aec5664
Added support for hidden fields, fixed validation bug which limited validation rules to one.

git-svn-id: https://plugins.svn.wordpress.org/wpgform/trunk@801501 b8457f37-d9ea-0310-8a92-e5e31aec5664
Prep for v0.59 release.

git-svn-id: https://plugins.svn.wordpress.org/wpgform/trunk@801502 b8457f37-d9ea-0310-8a92-e5e31aec5664
Language translation files updated.

git-svn-id: https://plugins.svn.wordpress.org/wpgform/trunk@801503 b8457f37-d9ea-0310-8a92-e5e31aec5664