- read all joystick files from $FG_ROOT/Input/Joysticks automatically

- read all joystick files from $FG_ROOT/Input/Joysticks automatically
  (no need to list the paths explicitly in $FG_ROOT/joysticks.xml any more)
- move identified js nodes to /input/joysticks/js[0-9], but
- don't overwrite already set joystick data there
- remove all nodes when they aren't used any more
- add "id" node, which contains the js id that lead to the selection
  of a "named js" config
- add "source" node containing the path of the used js config file
- execute all nasal script groups at initialization time