add combine config for metrics in pivot table (#3086)

* add combine config for metrics in pivot table

* change method to stack/unstack

* update backendSync

superset/assets/javascripts/explore/stores/controls.jsx

@@ -249,6 +249,14 @@ export const controls = {
     description: 'Sort bars by x labels.',
   },
 
+  combine_metric: {
+    type: 'CheckboxControl',
+    label: 'Combine Metrics',
+    default: false,
+    description: 'Display metrics side by side within each column, as ' +
+    'opposed to each column being displayed side by side for each metric.',
+  },
+
   show_controls: {
     type: 'CheckboxControl',
     label: 'Extra Controls',

superset/assets/javascripts/explore/stores/visTypes.js

@@ -337,7 +337,7 @@ export const visTypes = {
         controlSetRows: [
           ['groupby', 'columns'],
           ['metrics', 'pandas_aggfunc'],
-          ['number_format', 'pivot_margins'],
+          ['number_format', 'combine_metric', 'pivot_margins'],
         ],
       },
     ],