Added apply_filters to uajax_result

Allows for developer to define their own template. This is the way I used a theme's existing template with respect for an existing post_type. 

```
function my_load_template($template) {
	global $post;
    ob_start();
    include($template);
    $var = ob_get_contents();
    ob_end_clean();
    return $var;
}


function my_result_template() {
	global $post;
	return my_load_template(get_template_directory().'/some-posttype-loop.php');
}
add_filter('uwpqsf_result_template', 'my_result_template');
```

You can see my alteration in action [here](http://digitalmined.com/courses/) (and why this functionality is absolutely necessary!)

It should be noted, however, this does no respect different search query forms. It is likely users would like to use a different templates for different forms.

This can be rectified by creating a more robust solution that has callbacks such as 
```
uwpqsf_result_template_3342
```