Fix missing texture for 90kph viaduct branch.

allow higher speeds in curves. As it turns out the previously accepted 'realistic' curve factor was for the highest cant but not feeling any sideway force.
However, you cannot recreate all real life curves, IRL there will be some sideway forces too. Hence the increase.

Made overpasses cheaper
Made stations cheaper

Added clamps to my sleeper textures (thanks LVSKB and Sir Ludicrous for the idea)
Removed the brown texture from intersecting rails.
Made the radius vs max speed more realistic.

Updated tunnel and bridge graphics to be merged to a single tunnel/bridge when building two parallel tracks. (kudos to LVSKB for figuring this out!)