[DENIED] ability to spawn trailers

[Chevy_Corbet#7999]

add the ability to spawn ONE trailer with a semitruck in freemode
On the options bar of the vehicle section add a slider like the one that is used to choose the vehicles that is available only when there is a vehicle classed as a towing vehicle (pickups and other small vehicles with a ball tow count as well, tow trucks don't).
The roleplay part of the freemode gamemode would be better and this gives room to other minigames as well.