Enable column formatting via templates

It gives an ability to move `html` from `Model.column_formatters`

Instead of doing

```python
column_formatters = {
    'title': lambda view, c, obj, attr: obj.title: Markup(u'<strong>%s</strong>' % obj.title))
}
```

you can do in list template:

```html
{% macro title(item) %}
    <strong>{{ item.title }}</strong>
{% endmacro %}
```