Add an option to change fps in enhanced menu

[Jolka248]

I noticed stuttering when i tested the nuclear power plant map. I got a 144 Hz display but in dgvoodoo.conf FPSLimit is set to 60. When i changed it to 144 it ran absolutely smooth. I would love to see an option to change the fps limit in the menus.

[Joshhhuaaa]

High FPS breaks things like the objective bar you mentioned in another discussion. It can also potentially ruin AI patrol routes, which is why I recommend 60 FPS. I agree it would be a good improvement to let the user change it in the menus though.