MAGETWO-32484: Stabilization of changes and bug fixing

- Add requirejs-config to newsletter template preview page

Author: Denys Rul

app/code/Magento/Newsletter/view/adminhtml/layout/newsletter_template_preview.xml

@@ -15,6 +15,7 @@
                 <block class="Magento\Newsletter\Block\Adminhtml\Queue\Preview\Form" name="preview_form"/>
                 <block class="Magento\Backend\Block\Store\Switcher" name="store_switcher" template="Magento_Backend::store/switcher.phtml"/>
             </block>
+            <block class="Magento\RequireJs\Block\Html\Head\Config" name="requirejs-config"/>
         </referenceContainer>
     </body>
 </page>