Javafx cleanup

I did a small clean up for rounding off the JavaFX migration. 

I looked closer into using JavaFX properties and bindings more, but found it not worth the effort trying to port the *working* code to use bindings. However, we may/should review this again with Java8.

We still need to handle multiple downloads and general download worker threading a bit better, but I'd like to see how we can incorporate the [ModuleManager](https://github.com/MovingBlocks/ModuleManager) for this task.

Closes #133