Look into simplifying the process of making custom controls

[ruckustboom]

There is a lot of boilerplate to making custom controls in JavaFX, especially when it comes to making integrating CSS and custom skinning. It would be nice if we could find a way to reduce as much of this as possible.

It might be worth while to have this as a separate library that can work well with normal JavaFX, potentially making it the goto for custom controls and a gateway to TornadoFX.

[pwittchen]

There's a typo in the issue title: "siplifying" ➡️ "simplifying".