Run Tests on Travis CI

Would it not be cool to run the tests automatically in [Travis CI](https://travis-ci.org/)? I have built a config to do so. It installs a neo4j server with gremlin plugin and executes the tests on every push / PR...

**To be done after eventual merge:**
- Create the main project on travis-ci.org (Must be done by the repo owner / [example from my fork](https://travis-ci.org/frne/Neo4j-PHP-OGM))
- Fix Tests / make them run on Travis
- Add fancy Button to readme like this... [![Build Status](https://travis-ci.org/frne/Neo4jUserBundle.svg?branch=1.0.0)](https://travis-ci.org/frne/Neo4jUserBundle)