Squid: Avoid cycle between java packages

Changed EventListenerRegistry (impl) to EventListenerRegistryService
(interface)
(forced by changes in http://review.motechproject.org/#/c/3279/)

https://trello.com/c/A0rrIWb0

Change-Id: I8f2f137f0f2e60cefde0a10dc2d648f2277be807
Merge "Squid: Avoid cycle between java packages"