Make API calls fail better

[rdohms]

API calls that require an admin key should fail more gracefully.

[pascaldevink]

Can't this be fixed in the \DMS\Service\Meetup\AbstractMeetupClient?
Or should it really be fixed with a try/catch in `AmsterdamPHP\Bundle\MeetupBundle\Service\EventService->getEventAttendance()`` for example?
Because than it would be nice if we have a list of calls that require admin permission so it's more clear what needs to be done.

[rdohms]

Not 100% sure where its best to handle this.
We need to check the calls and the problems and see how the API responds. I can add it to the api wrapper to at least make sure we have proper exceptions to handle.

[rob-erwt]

This issue is bugging me right now, so I'll try and fix it :P

[pascaldevink]

This should be right up @ramondelafuente's alley! Now only #45 has to be done to completely satisfy him 😜

[pascaldevink]

Fixed in #74