Changes to FXMLView logging and autoloading of javafx binary css files

[koppor]

This PR missors AdamBien#68.

I've really loved using afterburner.fx and I use it for several work projects. There were a few small things that were issues for me which I addressed in my own branch, but I wanted to offer them back into the main repository. The first thing was to change the logging messages in afterburner.fx so that they don't log to System.err. We have had bug reports from customers that think something is wrong because it can't find the css files for all views. The other change I made was to allow the loading of binary css files that javafx produces, we have a few large css files and the ability to use the binary format is important for us.
I implemented a set of tests to check the functionality as well and discovered a small bug in the css loading functionality. When getView() is called multiple times, the css sheet is added multiple times as a reference. I added a check to only add the css/bss files when they haven't already been added.

This is my first proper pull request, so I'm aware I might not be following etiquette, please provide feedback on the pull request if appropriate.

In @JabRef, we need a maintained version of afterburner.fx. We did it at https://github.com/JabRef/afterburner.fx. Now we saw activity here and would be happy to contribute our improvements here (and then delete our own fork).

[koppor]

Much more done at https://github.com/JabRef/afterburner.fx, thus closing this out.