Added support for HTML5 placeholders on text input values.

git-svn-id: https://plugins.svn.wordpress.org/wpgform/trunk@759529 b8457f37-d9ea-0310-8a92-e5e31aec5664
Prep for v0.56 release.

git-svn-id: https://plugins.svn.wordpress.org/wpgform/trunk@759530 b8457f37-d9ea-0310-8a92-e5e31aec5664