Freightliner Cascadia Truck 2018 fix v1.8

Changes 1.8: Improved glass def files Adjusted glass locators Removed incorrect engined Added correct engine Added corresponding gearboxes Cleanup of textures Cleanup of models Corrected the cabins to be recognised as cabines Added additional Flow Below mudguards Added better icons for parts Separated spoilers from cabs and added them as accessories various bug fixes Changed DD engine sound to Mercedes