Added Feature: getFileCallback option for client widget working

I was trying to use the option getFileCallback documented here:

https://github.com/Studio-42/elFinder/wiki/Client-configuration-options#wiki-getFileCallback

I've changed your EzzeElfinder.init function to get the chance of embed code like this in the options array for your **ElFinderWidget**

```PHP
$this->widget("application.common.extensions.ezzeelfinder.ElFinderWidget",
  array(
         'getFileCallback' => "console.log(file);",
  )
);
```

If **wysiwyg** option is defined too, getFileCallback takes preference.

My best regards.