re-added grid-rendering to the editor

rebuild grid/navMesh 3D data only if needed

mapview/3D/navMesh/NavMeshModel.h

@@ -24,6 +24,7 @@ private:
 	NM::NavMesh<NM::NavMeshTriangle> navMesh;
 	NM::NavMeshSettings settings;
 	Floorplan::IndoorMap* im;
+	int buildID = 0;
 
 public:
 
@@ -65,6 +66,10 @@ public:
 
 	};
 
+	int getBuildID() const {
+		return buildID;
+	}
+
 	void rebuild(Floorplan::IndoorMap* im) {
 
 		Listener l;
@@ -77,6 +82,8 @@ public:
 			fac.build(im, &l);
 		}
 
+		buildID = rand();
+
 	}
 
 };