Frontend Preview Hook

Add a Hook to manipulate the front end Preview query string.

Usage Example:
```php
public function SetFrontendPreview($strFrontendFile, $strDo, $intCurrentID)
{
	if ($do === "module1")
	{
		strFrontendFile = "?page=123";
	}
	if ($do === "module2")
	{
		strFrontendFile = "?page=234";
	}
	return $strFrontendFile;
}
```

This feature is a good improvement for all Modules, if they need to manipulate the front end preview.