long running rest requests

[rizen]

This could be a good way to handle things like the image uploads that are pending processing, or ving jobs.

POST /api/v1/whatever

return:
202 Accepted
Location: /api/v1/whatever/status/99

---

GET /api/v1/whatever/status/99

return:
303 See Other
Location: /api/v1/whatever/99
{ secondsToComplete: 33, percentComplete: 45 }