verify reference delete, modified test for it

src/story_tests/delete_reference.robot

@@ -10,6 +10,7 @@ Deleting a Reference Should Remove It From The List
     ${normal}=  Run Keyword And Return Status    Element Should Be Visible   id=view_normal_format
     Run Keyword If    ${normal}    Click Normal Button If Shown
     Click Button  Delete
+    Alert Should Be Present
     Go To References List Page
     Page Should Not Contain  Kernighan, Brian and Ritchie, Dennis
 

src/templates/reference_list.html

@@ -73,7 +73,7 @@ <h2 style="padding-top: 30px;">References</h2>
             <button type="submit" class="btn btn-primary">Edit</button>
           </form>
           <form action="/delete_reference/{{ reference[0] }}" method="post">
-            <button type="submit" class="btn btn-danger">Delete</button>
+            <button type="submit" class="btn btn-danger" onclick="confirmDelete(event, this.form)">Delete</button>
           </form>
         </div>
       </li>  
@@ -148,7 +148,9 @@ <h2 style="padding-top: 30px;">References</h2>
 </div>
 
 <script>
-  function confirmDelete(form) {
+  function confirmDelete(event, form) {
+    event.preventDefault();
+
     if (confirm("Are you sure you want to delete this reference?")) {
       form.submit();
     }