Define the max kart number of all game modes in config

[kimden]

Description

Currently the maximum possible number of karts for most modes (excluding racing) is hardcoded, for example, in tracks/track.cpp. This could be stored in the config files for all modes except those with one player, like ghost replay more or egg hunt.

[qwertychouskie]

For that matter, is there any reason why Egg Hunt couldn't be played online, perhaps in a time-attack format? Maybe it's best to open a new issue for that though.