Inform players about AI and other players waiting

Server config have settings `maxAiOpponents` (default 15). It's allows to limit active AI games. BUT user's don't known about that -- if you start new game with AI, but all AI opponets will be busy then your game is freeze on startup (empty battlefield) and unfreeze on AI available again.

There is must be message inform to players about AI busy status (or multiple messages -- every 1 minute as example). Also need to test timeouts for players with AI -- I can see timeouts for players like on rush hour (I think it's can be AI waiting timeouts with wrong priority time -- e.g. AI is waiting but server actived user's timeout):
```
ERROR 2019-04-21 19:55:44,179 ERROR - game freezed in waitResponseOpen for user xxx (connection problem) =>[CALL main-1500] HumanPlayer.waitResponseOpen
ERROR 2019-04-21 19:55:44,780 ERROR - game freezed in waitResponseOpen for user xxx (connection problem)
```

TODO:
* [ ] make feedback messages or waiting panel;
* [ ] test priority and timeouts with AI busy (it's can be limit maxAiOpponents to 1 for testing).
* [ ] make same feedback messages/panel for other players, not AI (e.g. one player started, but other disconnected before begin).