- modified the ToolDB class and changed some strings
- Preferences classes now have access to the App attributes through app.setup_obj_classes() method
- moved app.setup_obj_classes() upper in the App.__init__()
- added a new Preferences setting allowing to modify the mouse cursor color
- remade the GUI in Preferences -> General grouping the settings in a more clear way
- made available the Jump To function in Excellon Editor
- added a clean_up() method in all the Editor Tools that need it, to be run when aborting using the ESC key