Add SFall Misc->MainMenu*OffsetX/Y

[wipe2238]

https://github.com/sfall-team/sfall/blob/6b97ad4bcf6a2c57488a78d30e15a2e87074e50c/sfall/Modules/MainMenu.cpp#L76-L97
https://github.com/sfall-team/sfall/blob/6b97ad4bcf6a2c57488a78d30e15a2e87074e50c/sfall/Modules/MainMenu.cpp#L42-L57
https://github.com/sfall-team/sfall/blob/6b97ad4bcf6a2c57488a78d30e15a2e87074e50c/artifacts/ddraw.ini#L580-L584

Note that it requires modders to go back to "classic" way of changing menu position, by moving buttons backgrounds directly in mainmenu.frm.

That's a bit different from "modern" solution, where HRP provides main menu graphic and buttons background as separate .frms packed into f2_res.dat, and adds them dynamically basing on button position and own offset setting. At least that's how i understood whole thing works. I skipped whole HRP part for now to avoid adding .dat as dependency; menu offsets are not important enough to justify that at this point imho.

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Idea for future: once CE gets its own config, all of offset settings could be packed into one option. Instead of multiple settings...

MainMenuOffsetX=392
MainMenuOffsetY=26
;MainMenuCreditsOffsetX=0
;MainMenuCreditsOffsetY=0

...it could be just one with multiple values...

MainMenuOffsets=392 26 0 0 0 0

...which would handle copyright (1st and 2nd value), version (3rd and 4th, not present in current SFall), and menu (5th and 6th).