Change of color player kart when any player quits

@auriamg 
Two problems solved in commit 22
1> Params is now a pointer and behaving properly(even if a player goes back after coming to multiplayer screen, other screens are not affected)(see line 1225 in skin.hpp) 
2> If a player quits, color of karts will change accordingly.
if this is okay, then i will send the pull request.