[FIX] website: fix opening of the SelectEditMenuDialog

When on a page event for example, when the user choose "Edit menu",
a modal is first opened to ask which menu to edit (the top menu or
the event menu ?).

This feature was broken with a web_editor refactoring. Indeed, the
dialog was converted to use the standard dialog class but the
widget was still inserted in the DOM thanks to "appendTo" instead of
the modal built-in "open" method, preventing it to be properly opened.

addons/website/static/src/xml/website.contentMenu.xml

@@ -22,11 +22,13 @@
         </ul>
     </li>
 </t>
-<select t-name="website.contentMenu.dialog.select" class="form-control mb16" t-if="widget.roots">
-    <t t-foreach="widget.roots" t-as="root">
-        <option t-att-value="root.id"><t t-esc="root.name"/></option>
-    </t>
-</select>
+<div t-name="website.contentMenu.dialog.select">
+    <select class="form-control mb16" t-if="widget.roots">
+        <t t-foreach="widget.roots" t-as="root">
+            <option t-att-value="root.id"><t t-esc="root.name"/></option>
+        </t>
+    </select>
+</div>
 <div t-name="website.contentMenu.dialog.edit">
     <select class="form-control mb16" t-if="widget.roots">
         <t t-foreach="widget.roots" t-as="root">