Simplify option menu(s)

[colingeniet]

I propose the following changes to the option menus:

• Remove the FCS gearing/limiter/damping options. I don't think that they are supposed to be disabled on the real aircraft.
• Replace the buttons with checkboxes and sliders as appropriate, to make the UI easier to use.
• Merge the MP option menu with the main option menu.

On the technical side, is there a reason to keep the main option menu generated by Nasal/options.nas, instead of an xml dialog? I think the latter would be just as good and simpler.

[NikolaiVChr]

No reason, no.

[colingeniet]

I changed the menu as described, please tell me if you have any issue with the new one.