Monorail Curves

This isn't ready for release, but wanted to show some of the fun from my monorail branch:

Slowly getting monorail bezier curves right :-) The city subway map of the skies.

The towers/stations are fixed on the build grid, but the rail links are not. They're currently 9m high which is 2m above the tallest pneumatic tube tower but well below the Zeppelin and Blimp flight layers.

Rails will connect towers like coloured routes connect vehicle waypoints, and monorail cars just follow their colour. The fluro-green is a placeholder. As with vehicles, the control of vehicle routing is encoded in the routes themselves, not in each vehicle. 

At stations, monorail cars will physically pickup or unload a container, so we can use shipping containers more like IRL.