Check either user submitted HTML or displayed HTML

Currently, we only check accessibility of content on node submission through a hook in the form's validation. For some people using markup or WYSIWYG editors (or filters that remove or introduce more problems), it makes more sense to wait until the node is made, then check by using node_view() on the node.

This should be an option that is switched by the admin in the node_type form. The option would be "check on node submission" or "check after node has been saved." If the latter were picked, then the option of preventing saving a node for severe failures would be disabled.