Update widgets.py

How about adding those additional values to the template context? This allows having more options on how to render templates.
For example something like bootstrap tabs:
```
<!-- Nav tabs -->
<ul class="nav nav-tabs" role="tablist">
  <li class="nav-item">
    <a class="nav-link active" data-toggle="tab" href="#edit-{{attrs.id}}" role="tab">Edit</a>
  </li>
  <li class="nav-item">
    <a class="nav-link" data-toggle="tab" href="#preview-{{attrs.id}}" role="tab">Preview</a>
  </li>
</ul>

<!-- Tab panes -->
<div class="tab-content markdownx">
  <div class="tab-pane active" id="edit-{{attrs.id}}" role="tabpanel">
    {{ markdownx_editor }}
  </div>
  <div class="tab-pane" id="preview-{{attrs.id}}" role="tabpanel">
    <div class="markdownx-preview"></div>
  </div>
</div>
```

markdownx/widgets.py

@@ -71,6 +71,9 @@ class MarkdownxWidget(forms.Textarea):
 
         return template.render({
             'markdownx_editor': widget,
+            'name': name,
+            'value': value,
+            'attrs': attrs,
         })
 
     @staticmethod