webkit2: set GtkWidget as the parent of WebKitWebView
webkit-web-view-class: subclass gtk-widget
register-object-type fails

Complains that WebKitWebView already exists;
calling webkit-web-view-new just hangs.
webkit-web-view-new: return a webkit-web-view-class
webkit-web-view-new-with-context: return webkit-web-view-class