[IMP] website: allow custom classes in publish short button

Purpose is to be able to somehow control the display of publish buttons.
Indeed in some bases you want for example to display small buttons that
takes less place than current standard bootstrap button.

addons/website/views/website_templates.xml

@@ -468,8 +468,8 @@
 <template id="publish_short">
     <t groups="website.group_website_publisher" t-ignore="true">
         <div t-attf-class="float-right js_publish_management #{object.website_published and 'css_published' or 'css_unpublished'}" t-att-data-id="object.id" t-att-data-object="object._name" t-att-data-controller="publish_controller">
-            <button class="btn btn-danger js_publish_btn">Unpublished</button>
-            <button class="btn btn-success js_publish_btn">Published</button>
+            <button t-attf-class="btn btn-danger js_publish_btn #{additionnal_btn_classes or ''}">Unpublished</button>
+            <button t-attf-class="btn btn-success js_publish_btn #{additionnal_btn_classes or ''}">Published</button>
         </div>
     </t>
 </template>