title: Odoo 10 how to replace inherited qweb template content
body: <p>I have tried to insert a tag into an existing template but couldn't get it to work.</p>
  
  <p>Existing template in odoo/addons/mail/static/src/xml/thread.xml</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;templates xml:space="preserve"&gt;
  
      &lt;t t-name="mail.ChatThread"&gt;
          &lt;t t-if="messages.length"&gt;
             :
      &lt;t t-name="mail.ChatComposer.Attachments"&gt;
          &lt;div class="o_attachments"&gt;
              &lt;t t-foreach="attachments" t-as='attachment'&gt;
                  &lt;t t-call="mail.Attachment"&gt;
                      &lt;t t-set="editable" t-value="true"/&gt;
                  &lt;/t&gt;
              &lt;/t&gt;
          &lt;/div&gt;
      &lt;/t&gt;
  
      &lt;t t-name="mail.Attachment"&gt;
          &lt;div t-attf-class="o_attachment #{attachment.upload ? 'o_attachment_uploading' : ''}" t-att-title="attachment.name"&gt;
  
              &lt;a class="o_image" t-att-href='attachment.url' target="_blank" t-att-data-mimetype="attachment.mimetype" t-attf-data-src="/web/image/#{attachment.id}/100x80"&gt;
                  &lt;span class='o_attachment_name'&gt;&lt;t t-esc='attachment.name'/&gt;&lt;/span&gt;
              &lt;/a&gt;
              &lt;t t-if="editable"&gt;
                  &lt;div class="o_attachment_delete"&gt;
                      &lt;i class='fa fa-times-circle' title="Delete this attachment" t-att-data-id="attachment.id"/&gt;
                  &lt;/div&gt;
                  &lt;div class="o_attachment_progress_bar"&gt;
                      Uploading
                  &lt;/div&gt;
              &lt;/t&gt;
          &lt;/div&gt;
      &lt;/t&gt;
  </code></pre>
  
  <p>My custom template (odoo/addons/mycustom/static/src/xml/thread.xml):<br>
  I want to insert the Hello world after the class o_image in the original template.</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;templates xml:space="preserve"&gt;
      &lt;t t-name="mycustom.ImageAttachment" t-extend="mail.Attachment"&gt;
          &lt;t t-jquery="o_image" t-operation="append"&gt;
              &lt;div&gt;Hello world&lt;/div&gt;
          &lt;/t&gt;
      &lt;/t&gt;
  &lt;/templates&gt;
  </code></pre>
  
  <p>My javascript to render the template (odoo/addons/mycustom/static/src/js/thread.js):</p>
  
  <pre class="lang-js prettyprint-override"><code>odoo.define('mycustom.thread', function (require) {
  "use strict";
  
  var core = require('web.core');
  var ajax = require('web.ajax');
  var qweb = core.qweb;
  
  ajax.loadXML('/mycustom/static/src/xml/thread.xml', qweb);
  console.log("INFO", "Hello World")
  
  });
  </code></pre>
  
  <p>My assets file (odoo/addons/mycustom/views/assets.xml):</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;odoo&gt;
      &lt;template id="assets_backend" name="my assets" inherit_id="web.assets_backend"&gt;
        &lt;xpath expr="." position="inside"&gt;
            &lt;script type="text/javascript" src="/mycustom/static/src/js/thread.js"&gt;&lt;/script&gt;
        &lt;/xpath&gt;
      &lt;/template&gt;
  &lt;/odoo&gt;
  </code></pre>
  
  <p>My manifest file (odoo/addons/mycustom/<strong>manifest</strong>.py):</p>
  
  <pre class="lang-py prettyprint-override"><code># -*- coding: utf-8 -*-
  {
      'name': "test",
      'summary': """my test""",    
      'description': """
          This is my test module.
      """,
      'author': "peter",
      'website': "",
      # Categories can be used to filter modules in modules listing
      # Check https://github.com/odoo/odoo/blob/master/odoo/addons/base/module/module_data.xml
      # for the full list
      'category': 'Test',
      'version': '0.1',
      # any module necessary for this one to work correctly
      'depends': ['base','mail'],    
      # always loaded
      'data': [
          'views/assets.xml',
      ],
      'qweb': [
          'static/src/xml/thread.xml',
      ],        
  }
  </code></pre>
  
  <p>The javascript is loaded because I can see the text <code>Hello World</code> written on the browser console.
  However, I cannot see the <code>&lt;div&gt;Hello World&lt;/div&gt;</code> in the chat thread. What did I miss?</p>