[fb] filechooser.js should not always open on / by default

The usability is pretty annoying currently as clicking on the filechooser always opens on the root.

It would be nice if we could pick the path the filechooser plugin should open on. The decreasing priorities could be:

1. load the input path it is linked too
2. load the previously opened directory
3. load the home directory of the user
4. load / (current behavior)

This should reflect on all the apps using the plugin (Filebrowser/Job designer/Beeswax...).