add multicategory + mirror ax mock

Author: etpinard

test/image/baselines/multicategory-mirror.png

@@ -0,0 +1,34 @@
+{
+  "data": [
+    {
+      "type": "bar",
+      "x": [
+        ["2017", "2017", "2017", "2017", "2018", "2018", "2018"],
+        ["q1", "q2", "q3", "q4", "q1", "q2", "q3" ]
+      ],
+      "y": [1, 2, 3, 1, 3, 2, 3, 1]
+    },
+    {
+      "type": "bar",
+      "x": [
+        ["2017", "2017", "2017", "2017", "2018", "2018", "2018"],
+        ["q1", "q2", "q3", "q4", "q1", "q2", "q3"]
+      ],
+      "y": [1.12, 2.15, 3.07, 1.48, 2.78, 1.95, 2.54, 0.64]
+    }
+  ],
+  "layout": {
+    "xaxis": {
+      "ticks": "outside",
+      "showline": true,
+      "mirror": "ticks",
+      "zeroline": false
+    },
+    "yaxis": {
+      "showline": true,
+      "ticks": "outside",
+      "mirror": "ticks",
+      "range": [-0.5, 3.5]
+    }
+  }
+}