Add class attributes to some filters to get better CSS selector access.

To get better CSS selector access to all filter results, a class attribute to every filter has been added:

**Youtube Link**

```
<iframe class="auto-html-iframe youtube-iframe" ...
```

**Vimeo Link**

```
<iframe class="auto-html-iframe vimeo-iframe" ...
```

Some filters requires a prepend 'span' tag with the class attribute. The fact that 'div' tags are not allowed inside 'p' tags we use 'span' tags to add the class attribute.