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

world/TrkFoll.h

@@ -49,6 +49,7 @@ public:
   private:
 // methods
     bool ComputatePosition(); // przeliczenie pozycji na torze
+    int JoinedEnd( int const End ) const;
 // members
     TTrack *pCurrentTrack = nullptr; // na którym torze siê znajduje
 	std::shared_ptr<TSegment> pCurrentSegment; // zwrotnice mog¹ mieæ dwa segmenty
@@ -58,6 +59,9 @@ public:
     int iEventFlag = 0; // McZapkie-020602: informacja o tym czy wyzwalac zdarzenie: 0,1,2,3
     int iEventallFlag = 0;
     int iSegment = 0; // który segment toru jest używany (żeby nie przeskakiwało po przestawieniu zwrotnicy pod taborem)
+    int iPath = -1; // the path of the switch the axle runs on
+    double fTrailAt = -1.0; // coming from the frog end of a switch: where along the path the wheels push the blades over
+
 };
 //---------------------------------------------------------------------------
 #endif