add three cone mocks

- unfortunately they don't render correctly in `imagetest`

Author: etpinard

test/image/baselines/gl3d_cone-simple.png

@@ -0,0 +1,33 @@
+{
+  "data": [
+	{
+	  "type": "scatter3d",
+	  "mode": "markers",
+      "x": [1, 2, 3],
+      "y": [1, 2, 3],
+      "z": [1, 2, 3]
+	},
+    {
+      "type": "cone",
+      "x": [1, 2, 3],
+      "y": [1, 2, 3],
+      "z": [1, 2, 3],
+      "u": [0.1, 0, 0],
+      "v": [0, 0.3, 0],
+      "w": [0, 0, 0.2]
+    }
+  ],
+  "layout": {
+    "scene": {
+      "xaxis": {
+        "range": [-2, 5]
+      },
+      "yaxis": {
+        "range": [-2, 5]
+      },
+      "zaxis": {
+        "range": [-2, 5]
+      }
+    }
+  }
+}