feat(track): 3D sleepers and switch timbers, blade heel and throw from templates, one rail carving pass

- sleepers3d / sleepers3dplain / sleepers3dbed in eu07.ini: timbers put together from the begin, main and end parts of a model
  and stretched to their length, plain sleepers of their own model; tracks whose plain sleepers would touch are laid as one
  cluster, lines of timbers led by priority and turned to the bisectors of frogs and crossings at a limited rate, whole timbers
  under crossings, split ones between tracks with room to part them, gaps filled per rail and overlaps shortened or dropped;
  clusters worked out in a background thread while driving, on demand in the editor
- the ballast can be left out under the beams (sleepers3dbed no)
- blades get their heel and throw from the switch template or blades <heel> <throw> in the scenery; blades of double switches
  run on into the track linking them to the next switch
- rail cutting at frogs, wing rails, movable noses and switch crossings done by one carving pass (RailCarve)
- tint of the rail treads applied to the colour only, without the matte band at the frog
- a switch trailed through with a movable nose set the other way derails the vehicle
- self-tests: sleepercheck, sharedzones, beamsnear, throw, sleepersbg

application/editormodeconnection.cpp

@@ -313,7 +313,7 @@ void editor_mode::insert_connection()
 		auto second{glm::normalize(plan_of(plan.ends[3] - plan.ends[2]))};
 		if (glm::dot(first, second) < 0.0)
 			second = -second;
-		auto const parts{build_double_slip(plan.ends[0], plan.ends[1], plan.ends[2], plan.ends[3], plan_of(plan.centre), plan.centre.y, first, second, plan.angle, 0.0, *style, "Skrz")};
+		auto const parts{build_double_slip(plan.ends[0], plan.ends[1], plan.ends[2], plan.ends[3], plan_of(plan.centre), plan.centre.y, first, second, plan.angle, editor_track::slip_curve{}, *style, "Skrz")};
 		editor_track::commit(parts);
 		created.insert(created.end(), parts.begin(), parts.end());
 	}