API service edits should support parent_service references

[abellotti]

While we support specifying parent_id when editing a service via POST /api/services/:id, API should support the parent_service reference signature (href or id) like it does for create:

Example:

POST /api/services/:id

{
   "action" : "edit",
   "resource" : {
       "parent_service" : { "href" : "http://localhost:3000/api/services/10" }
   }
}