Best packaging practices (Debian Dev Manual)

According the [Debian Packaging Manual] (http://www.debian.org/doc/manuals/developers-reference/best-pkging-practices.html):

- "Be sure that a purged package is completely gone, that is, it must remove any files created, directly or indirectly, in any maintainer script".

So, with this pull request, we have now a script that cleans all changes when the package is purged