`yii\widgets\Breadcrumbs` enhacement

I have markup:
```html
<ul class="page-breadcrumb breadcrumb">
    <li>
        <i class="fa fa-home"></i>
        <a href="index.html">Home</a>
        <i class="fa fa-angle-right"></i>
    </li>
    <li>
        <a href="#">Dashboard</a>
    </li>
</ul>
```
And I want to use template for individual link. Now I can`t use it. This PR will allow to do this.