Added filter pass-through to shortcode HTML return

As discussed removed the HTML wrapping from the short code evaluator and allowed wrapping to be controlled by plugin users.

For example, to continue to add your wrapping div you'd simply add the following filter to a plugin/functions.php;

```php
#} Filter embed to wrap with required html.
function filter_embed($html) {
  $return = '<div class="samAsset">' . $html . '</div>';
  return $return;
}
add_filter( 'sam_embed', 'filter_embed');
```