Reviewer Mike - AbstractService API definition

Mike, the AbstractService API we have been discussing recently is very similar to the AppServer API we put together last sprint.  I've put the two APIs in the same file for ease of comparison, but in future I assume one will live in Sprout while the other will live in clearwater-app-servers.

I renamed `ServiceTsx` to `AppServerTsxHelper` to prevent clashes with the Service API.