Php parser

This is a work-in-progress towards fixing #195. Commits are still a bit messy, tests are still failing, code isn't completely cleaned up, but hopefully it can serve for some preliminary review or discussion. You have been warned ;-)
Well, taking vip-quickstart's dependency on vip-scanner into account, I'm yet again inclined to stick with git submodules for now.

To wrap up: if we were going to use composer, we would need to add extra (possibly manual) steps as part of vip-quickstart's setup; or, we could try to [automatize](https://github.com/tPl0ch/puppet-composer) that, which I think would be much preferrable.

But all that sounds like a rabbit hole in its own right, compared to using git submodules for now, which are automatically included when vip-scanner is `git pulled`, e.g. from within vip-quickstart.