Add custom map support to private lobbies

[RGG200]

I would like to be able to play on the maps I designed with friends and I thought other people may want that too so thought I'd suggest that.

[GeneralYazov]

Agree

[miroslav-pavlov]

This is impossible for FXClient as it is a client. It doesn't control the server to be able to choose custom maps.

[peshomir]

This is impossible for FXClient as it is a client. It doesn't control the server to be able to choose custom maps.

Actually, it is possible, as the custom lobbies use a custom reverse-engineered game server.