[Explore] applying refresh chart overlay when chart is stale (#4486)

* adding refresh chart overlay when chart is out of sync with control panel

* fading the visualization when stale

* addressing comments from team on layout of UI

superset/assets/javascripts/components/RefreshChartOverlay.jsx

@@ -0,0 +1,42 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import Button from '../components/Button';
+import { t } from '../locales';
+
+const propTypes = {
+  height: PropTypes.number.isRequired,
+  width: PropTypes.number.isRequired,
+  onQuery: PropTypes.func,
+  onDismiss: PropTypes.func,
+};
+
+class RefreshChartOverlay extends React.PureComponent {
+  render() {
+    return (
+      <div
+        style={{ height: this.props.height, width: this.props.width }}
+        className="explore-chart-overlay"
+      >
+        <div>
+          <Button
+            className="refresh-overlay-btn"
+            onClick={this.props.onQuery}
+            bsStyle="primary"
+          >
+            {t('Run Query')}
+          </Button>
+          <Button
+            className="dismiss-overlay-btn"
+            onClick={this.props.onDismiss}
+          >
+            {t('Dismiss')}
+          </Button>
+        </div>
+      </div>
+    );
+  }
+}
+
+RefreshChartOverlay.propTypes = propTypes;
+
+export default RefreshChartOverlay;