- Engines control now use the same axis methods as the flight controls; which allows for these to have an inverted checkbox.
- Change the axis combo boxes to instead show a popup dialog (much like the button config). This is better because the items can be grouped sensibly.
- Changed the way that the "all engines" controls work - the dialog binds these to a "engines/XXXX-all" for which there is a listener in controls.nas which propogates over all engines.
- Added extra bindings to both the buttons and the axis dialogs.
- moved the "None" button to the bottom and renamed it to the more comprehensible "Remove assignment"
