My group channels feature

[jkeam]

Addresses #12

[jkeam]

@GustavoCaso can you double check the keys in travis and in sendbird?

[jkeam]

@GustavoCaso

Would love to get this PR fixed up. Suggestions on fixing up the errors? I have a feeling something isn't set up right either in my test env or travis. I have a feeling the test user and test account previously used by travis aren't good anymore?

      Failure/Error: fail ApiKeyMissingError.new(api_key_message) unless api_key(app)
      
      Sendbird::Client::ApiKeyMissingError:
        Plase set up your applications and default_app