Get query button working in explorev2 (#1581)

* Get query buttonw working in explorev2

 - Create new endpoint for updating explore viz
 - Send over new form_data when query button is pressed

* Added endpoint test

* Changes based on comments

* Added docstring for endpoint, and query spec

* Remove white space around docstring

superset/assets/javascripts/explorev2/reducers/exploreReducer.js

@@ -68,6 +68,29 @@ export const exploreReducer = function (state, action) {
         { viz: Object.assign({}, state.viz, { form_data: newFormData }) }
       );
     },
+    [actions.UPDATE_CHART]() {
+      const vizUpdates = {
+        column_formats: action.viz.column_formats,
+        json_endpoint: action.viz.json_endpoint,
+        csv_endpoint: action.viz.csv_endpoint,
+        standalone_endpoint: action.viz.standalone_endpoint,
+        query: action.viz.query,
+        data: action.viz.data,
+      };
+      return Object.assign(
+        {},
+        state,
+        {
+          viz: Object.assign({}, state.viz, vizUpdates),
+          isChartLoading: false,
+        });
+    },
+    [actions.CHART_UPDATE_STARTED]() {
+      return Object.assign({}, state, { isChartLoading: true });
+    },
+    [actions.CHART_UPDATE_FAILED]() {
+      return Object.assign({}, state, { isChartLoading: false });
+    },
   };
   if (action.type in actionHandlers) {
     return actionHandlers[action.type]();