AI: server must support multi-threaded simulations (minimum one per game)

Current AI implementation uses single non-game thread for any calculations (game simulation). If you run multiple games with AI then each game must wait another (e.g. one freezes AI game can ruin whole AI games on server).

Possible reason: protection from concurrent data modifications or memory overflow;

What can be done:
* [x] normal: enable one AI thread per real game - it must be safe, even for ai vs ai games - it's done by max ai threads increase from 1 to 5;
* [ ] good: enable one thread per AI player - it’s better but may be affected by concurrent data modifications or other bugs. Can be implemented after more AI stability fixes.