Use native FileChooser (JavaFX) if possible

[miho]

Currently, the Swing JFileChooser is used. This is not optimal in many situations since expected features are missing. Only in situations where special functionality (like restricted file system view & navigation) is used, the Swing JFileChooser should be used.

[miho]

before:

after:

[miho]

Unfortunately, modal JavaFX in Swing applications don't seem to be possible right now :( We will probably leave the native option in the preferences. Let's see what users think...