Reworked cargo "Overcargo" for Scs flatbed in Ets2

Reworked cargo "Overcargo" for Scs flatbed in Euro Truck Simulator 2

Features:

This mod replace the cargo "overcargo", with a new one with ramps positioned inside the width of the flatbed.
Also a couple of straps are added on the ramps.
Work with vanilla flatbed, and modded trailer wich use the default cargo.