Use react-alert for backend message flashing (#3315)

superset/assets/javascripts/SqlLab/components/App.jsx

@@ -70,7 +70,7 @@ class App extends React.PureComponent {
     }
     return (
       <div className="App SqlLab">
-        <AlertsWrapper />
+        <AlertsWrapper initMessages={this.props.initMessages} />
         <div className="container-fluid">
           {content}
         </div>
@@ -82,11 +82,13 @@ class App extends React.PureComponent {
 App.propTypes = {
   alerts: PropTypes.array,
   actions: PropTypes.object,
+  initMessages: PropTypes.array,
 };
 
 function mapStateToProps(state) {
   return {
     alerts: state.alerts,
+    initMessages: state.flash_messages,
   };
 }
 function mapDispatchToProps(dispatch) {