[AIRFLOW-3569] Add "Trigger DAG" button in DAG page (/www only) (apac…

…he#4373)

This is a back-ported version of the change introducted to the RBAC ui
in apache#4373.

airflow/www/templates/airflow/dag.html

@@ -94,6 +94,13 @@ <h4 class="pull-right">
           Code
         </a>
       </li>
+      <li>
+        <a href="{{ url_for("airflow.trigger", dag_id=dag.dag_id, origin="/tree?dag_id="+dag.dag_id) }}"
+          onclick="return confirmTriggerDag('{{ dag.safe_dag_id }}')">
+          <span class="glyphicon glyphicon-play-circle" aria-hidden="true"></span>
+          Trigger DAG
+        </a>
+      </li>
       <li>
         <a href="{{ url_for("airflow.refresh", dag_id=dag.dag_id) }}" title="Refresh">
           <span class="glyphicon glyphicon-refresh" aria-hidden="true"></span>
@@ -330,6 +337,10 @@ <h4 class="modal-title" id="dagModalLabel">
       $("#dagModal").css("margin-top","0px");
     }
 
+    function confirmTriggerDag(dag_id){
+        return confirm("Are you sure you want to run '"+dag_id+"' now?");
+    }
+
     function confirmDeleteDag(dag_id){
         return confirm("Are you sure you want to delete '"+dag_id+"' now?\n\
           This option will delete ALL metadata, DAG runs, etc.\n\