Issue50 add mb external applications x

Add topic exchange / queue to as entry point for applications to produce messages that will trigger functionality within the Message Broker system. Binding key for queue to support multiple applications sending messages to the same exchange.

- Exchange: `directExternalApplicationsExchange`
- Queue: `externalApplicationEventQueue`
- Queue: `externalApplicationUserQueue`

- The first application: Celebrities Gone Good (CGG)
  - possible message routing keys:
    - cgg.user.register: User registration resulting in Drupal user creation and transactional email or sms
    - cgg.event.vote: Transactional email or sms