refactor(unitTests): use sinon to mock hidden itowns.Fetcher and add json file localy

Author: ftoromanoff

src/Process/3dTilesProcessing.js

@@ -272,7 +272,6 @@ export function process3dTilesNode(cullingTest = $3dTilesCulling, subdivisionTes
             return undefined;
         }
 
-
         // do proper culling
         const isVisible = cullingTest ? (!cullingTest(layer, context.camera, node, node.matrixWorld)) : true;
         node.visible = isVisible;

test/data/EGM2008_simplified.gdf

@@ -0,0 +1,59 @@
+       long_lat_unit     degree
+      latlimit_north       90.000000000000
+      latlimit_south      -90.000000000000
+      longlimit_west      -180.00000000000
+      longlimit_east       180.00000000000
+            gridstep       45.000000000000
+  latitude_parallels             5
+ longitude_parallels             9
+number_of_gridpoints            45
+         grid_format     long_lat_value
+
+          longitude    latitude    geoid
+            [deg.]      [deg.]         [meter]
+end_of_head ============================================
+          -180.0000     90.0000       15.303555275629
+          -135.0000     90.0000       15.303555275629
+           -90.0000     90.0000       15.303555275629
+           -45.0000     90.0000       15.303555275629
+             0.0000     90.0000       15.303555275629
+            45.0000     90.0000       15.303555275629
+            90.0000     90.0000       15.303555275629
+           135.0000     90.0000       15.303555275629
+           180.0000     90.0000       15.303555275629
+          -180.0000     45.0000       -5.932658849087
+          -135.0000     45.0000      -26.975163013039
+           -90.0000     45.0000      -33.177905776048
+           -45.0000     45.0000       28.384029129025
+             0.0000     45.0000       47.171595586227
+            45.0000     45.0000        1.250168904938
+            90.0000     45.0000      -57.850806052736
+           135.0000     45.0000       28.732846840211
+           180.0000     45.0000       -5.932658849086
+          -180.0000      0.0000       21.686023009812
+          -135.0000      0.0000       -6.357450314494
+           -90.0000      0.0000       -3.655670977408
+           -45.0000      0.0000      -22.874077173170
+             0.0000      0.0000       17.630240691122
+            45.0000      0.0000      -43.169258390344
+            90.0000      0.0000      -62.880767797666
+           135.0000      0.0000       73.143720247498
+           180.0000      0.0000       21.686023009809
+          -180.0000    -45.0000        3.784451421987
+          -135.0000    -45.0000      -14.624611735984
+           -90.0000    -45.0000       -0.474825154979
+           -45.0000    -45.0000       -3.262856182088
+             0.0000    -45.0000       21.392469069597
+            45.0000    -45.0000       46.285391983932
+            90.0000    -45.0000        8.143232184390
+           135.0000    -45.0000      -19.858291708014
+           180.0000    -45.0000        3.784451421987
+          -180.0000    -90.0000      -29.705396897506
+          -135.0000    -90.0000      -29.705396897506
+           -90.0000    -90.0000      -29.705396897506
+           -45.0000    -90.0000      -29.705396897506
+             0.0000    -90.0000      -29.705396897506
+            45.0000    -90.0000      -29.705396897506
+            90.0000    -90.0000      -29.705396897506
+           135.0000    -90.0000      -29.705396897506
+           180.0000    -90.0000      -29.705396897506