REST API Support for Service Requests as subcollections

- Supporting /api/service_templates/#/service_requests
- Supporting /api/service_templates/#/service_requests/#
- Supporting /api/service_templates/#/service_requests/# --expand=request_tasks
- Supporting /api/service_requests/#/request_tasks (or tasks)
Merge pull request #312 from abellotti/rest_api_service_requests_tasks

REST API Support for Service Requests as subcollections