Dutch translation

I saw a few other translations so I thought I add the Dutch translation as well, is easier for the end user to have it all in one package. We still have it in our repository at: https://github.com/dutch-translators I will add a note in the readme file with a note and link that the translations is added to the core after this pr is merged.
Can you remove this line, and add your info instead to a new line under neath `Advanced BBCode Box 3.1 [Dutch]`, like:

```
* Advanced BBCode Box 3.1 [German]
* Translated by Dutch Translators (https://github.com/dutch-translators)
*
* @copyright (c) 2013 Matt Friedman
* @license GNU General Public License, version 2 (GPL-2.0)
```