Ah, finally nailed optional `vbox` support for the...

# tornadofx

[edvin]

Ah, finally nailed optional vbox support for the Form builder. Now you can say field("Name", VERTICAL) { } and you'll be operating on a VBox instead of an HBox. Special support has also been added to support vgrow = Priority.ALWAYS to make for example a textarea inside a Form grow with the window.