Bugfixes and minor improvements:

Changes

• Added scenery preloading when continuing a saved run
• Fixed scenery preload to also load terrain
• Swapped second and third phase of scenery preloading
• Optimised first phase of scenery loading
• Sped up scenery item placement again
• Fixed missing rails in some routes
• Fixed roads not crossing tracks properly in some routes
• Fixed fences in the middle of the track in some routes
• Fixed route editor to update buildings bases
• Fixed missing bulkhead windows in some trains
• Fixed seat ends
• Enabled GUI zooming for editors