[explore] improve metric(s) and groupby(s) controls (#2921)

* [explore] improve metric(s) and groupby(s) controls

- surface verbose_name, description & expression in controls
- [table viz] surface verbose name in table header

* Fixing tests

* Addressing comments

* Fixing tests (once more)

superset/assets/javascripts/explore/components/ChartContainer.jsx

@@ -69,14 +69,15 @@ class ChartContainer extends React.PureComponent {
   getMockedSliceObject() {
     const props = this.props;
     const getHeight = () => {
-      const headerHeight = this.props.standalone ? 0 : 100;
+      const headerHeight = props.standalone ? 0 : 100;
       return parseInt(props.height, 10) - headerHeight;
     };
     return {
-      viewSqlQuery: this.props.queryResponse.query,
+      viewSqlQuery: props.queryResponse.query,
       containerId: props.containerId,
+      datasource: props.datasource,
       selector: this.state.selector,
-      formData: this.props.formData,
+      formData: props.formData,
       container: {
         html: (data) => {
           // this should be a callback to clear the contents of the slice container
@@ -128,10 +129,9 @@ class ChartContainer extends React.PureComponent {
       },
 
       data: {
-        csv_endpoint: getExploreUrl(this.props.formData, 'csv'),
-        json_endpoint: getExploreUrl(this.props.formData, 'json'),
-        standalone_endpoint: getExploreUrl(
-          this.props.formData, 'standalone'),
+        csv_endpoint: getExploreUrl(props.formData, 'csv'),
+        json_endpoint: getExploreUrl(props.formData, 'json'),
+        standalone_endpoint: getExploreUrl(props.formData, 'standalone'),
       },
 
     };
@@ -308,6 +308,7 @@ function mapStateToProps(state) {
     chartStatus: state.chartStatus,
     chartUpdateEndTime: state.chartUpdateEndTime,
     chartUpdateStartTime: state.chartUpdateStartTime,
+    datasource: state.datasource,
     column_formats: state.datasource ? state.datasource.column_formats : null,
     containerId: state.slice ? `slice-container-${state.slice.slice_id}` : 'slice-container',
     formData,