ExtraModMod version check

[joseasoler]

It should be possible to check the current ExtraModMod version in multiplayer games. ExtraModMod stores its version in the TXT_KEY_VERSION string. If that string could somehow be incorporated into the logic that determines when a game goes OOS (in the calculateSyncChecksum method), ExtraModMod would go OOS as soon as a player with a different game version connects.