The Vauxhall Tonic (every burp is nervous)

• LTN boundary selection can now split neighborhoods in most ways
• allow UK scenarios to be generated with one-shot imports
• fix pedestrian rendering crash that happened in some maps
• fix how cycle-and-foot-only roads are drawn unzoomed
• make LTN impact prediction tool stop running out of video memory
• internal refactoring to separate Scenario stuff from rest of simulation code