Added basic nginx support

Fixes #11.
Introducing nginx support with the help of puppet module jfryman/puppet-nginx.

Take a look at the `explode_and_quote` in manifest.pp.twig. This replaces the formatting in `PuppetModuleAbstract`. The Nginx class only explodes given entries to arrays but does no further formatting. 

The webserver is set to apache as default. As soon as the nginx tab is selected an hidden input field changes the webserver value accordingly.

If nginx is selected then the according puppet module (which is installed with composer.. and points currently to my fork) is added to the zip archive. In this way we could optimize the archive output for the user.

I also started to define `Puphpet\Domain\File` as service, preparing better testability for this class.

This PR requires this PR https://github.com/jtreminio/vagrant-puppet-lamp/pull/3 otherwise provisioning with nginx will not work because of incorrect referenced PHP services.

Currently only one vhost could be created. I just wanted to introduce nginx support with this PR. Any further nginx integration should be done later on.