add one more AUX slot

if there were 3 AUX slot in total, the game will be perfect. now we can install only two AUX, which isn't enough basically. why 3 AUX not 4 AUX, as 4 AUX isn't needed, 3 AUX have balance the difficulty and the fun of the gameplay, esp under heavy cop chasing a day.

however, limited the car only can equip two nitro boost only, not three in total. my idea is if we have three slot, i can install , mainly the stuff against or counter cop chasing tools, not nitro .