Allow configuration of allowed gamemodes

[ggtylerr]

In the demo video, it shows that the mod automatically disables when a user is in creative mode. While that's fine, having the option to disable that, or being able to configure what modes are allowed (like having spectator mode disable the anti-cheat, which would be incredibly helpful for mods) would be greatly appreciated.

Also, here's an obligatory "1.17 when" plea: wHenN's 1.17???/?