Edit mode undo

• better crosswalk generation when there's only a sidewalk on one side of a road
• edit mode UI revamp: paintbrush-style buttons to apply changes to lanes
• show error messages and prevent edits, like disconnecting sidewalks
• properly ban bikes from highways (revamped rules for vehicles using a lane)
• new freeform mode tool to spawn bikes
• WIP (not working yet): make bikes prefer bike lanes. some debug heatmaps for path cost
• edit mode has proper undo support