Add a save realism mode

[KJeff01]

Old work I had laying around from a suggestion. This introduces a "no manual saving" mechanism which I so far call "realism" and is available in the Game Options section. Probably a better name so I'll take any suggestions on that. You get just 1 autosave a second*** into a mission.

Quickload/quicksave disabled. Escape menu saving disabled. Debug mode disabled.

*** Due to how videos only get played the next tick after the scripts invoke a video call command, we need to delay it a bit so the videos get saved into the Intel menu.

[ManManson]

I haven't seen the "save realism" term anywhere else and it may not be clear for the majority of players what this mode actually does without providing a comprehensive description. I think a better alternative would be to call it "Autosave-only mode". This clearly describes the actual side-effect, so that only autosaves are allowed and nothing else (e.g. no manual saving, as intended).

Also, looks like debug mode accessibility should not be affected, because the main purpose of this mode is to actually debug something. If one happens to run into a bug while doing a Autosave-only walkthrough of a campaign map, he might have a hard time trying to easily set up a reproducer or at least understand what's happening without attaching with a debugger.

[KJeff01]

Pastdue added this to the campaign PR so this can be closed.