Refactoring how we find a service to execute

Based on @seanewest's feature-request/ideas around creating services from global modules see #48 , I'm working on some refactoring that will make service discovery easier:

1. I'm making it so we can filter by a service name when running any command.
2. Once I've done this, I'm going to make it so we fall-back to looking for a service.json in several places:
  * look for a local service.json.
  * fallback to `./node_modules`, `../node_modules`, etc, `/usr/lib/node_modules.`