Hydraulic Broken Trailer

Adds hydraulic condition and failure to tippable trailers. Each full lift/unload cycle wears the hydraulic. The HUD shows hydraulic OK and damage percentage. When the condition reaches 0%, the trailer body stays raised and Repair Hydraulic becomes available in the workshop. Partial damage can be restored with Service Hydraulic in the workshop. If the trailer is detached while raised/unloading, the body stays up until it is attached again.