Arbitrary HTML in Bootstrap Tab

* Package version: 1.8.1
* Django version: 3.0.2
* Python version: 3.7.3
* Template pack: bootstrap3

### Description:

Currently it's not possible to include, e.g., FontAwesome icons in a bootstrap3 tab. I was able to get it working by replacing `{{ link.name|capfirst }}` with `{{ link.name|safe }}` in `templates/bootstrap3/layout/tab-link.html` and then

```
self.helper.layout = Layout(
TabHolder(
Tab(
' Align Left',
Row(),
css_id='align-left',
),
),
)
```

I don't know if `|safe` becomes a security issue or if people don't think this functionality is needed, but I like to put icons in my tabs so I figured I'd suggest it to the community. Currently, with the `|capfirst` tag the tab will show the HTML as text instead of rendering the icon. Thoughts?