Upgrade OS (+Vbox Guest additions), Vagrantfile and puppetmodules

Vagrant upping did not work on newer versions of Virtualbox, as mentioned in several issues.
The fix was clear: upgrade the virtualbox guest additions for CentOS.

While @ramondelafuente published a fixed box, the downloadlink was very slow and he mentioned that we have yet to find a good location for that box.
While I was looking for a location to put it, it seems that PuppetLabs hosts recent versions of puppet-enabled CentOS distributions with up-to-date guest additions. But unfortunately they do not support CentOS 6.3 32bits anymore.

I've chosen to try their CentOS 6.4 64bit box, and after updating the puppet modules it works like a charm (for me).

## Related issues
https://github.com/protalk/protalk/issues/186
https://github.com/protalk/protalk/issues/195

## Known issues
I do still see a weird error when visiting the protalk.dev homepage: "Method Protalk\MediaBundle\Entity\MediaSpeaker::__toString() must not throw an exception".

However I don't think that is due to the new Vagrant configuration. Can anyone confirm that?

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When `vagrant up`ing an error occures during "set-xdebug-ini-values". As far as I know this doesn't affect the application.

## Todo list:
- [x] Moved external puppet modules into submodules
- [x] Updated Vagrantfile with a new virtualbox from PuppetLabs
- [x] Upgrade the external puppet modules to recent versions
- [ ] Update README

Could you all test this version, and see if it is a good replacement for the current Vagrant configuration?

I'm not very experienced with Vagrant, any feedback is welcome!