Group urlname configurable [issue #45]

Fix for issue AmsterdamPHP#45
- making the Meetup group URL name configurable
- abstracted the common behavior of the `*Service` classes

`.gitignore`
 - exclude IDE files (PhpStorm)
your personal files,like IDE choice, should be excluded using git's global config (http://stackoverflow.com/questions/7335420/global-git-ignore)