Adds API endpoint listing all operator shelves upon which the current user has permission to operate (bug 1074368).

![Mine.](https://cloud.githubusercontent.com/assets/23885/4565352/25abe82e-4f1f-11e4-866f-e56ec9b14b8a.gif)

r? @ngokevin @robhudson @diox 
Would be easier to read with:
```
query = Q()
for perm in perms:
    query |= Q(carrier=perm.carrier, region=perm.region)
```

In any case, what happens if the user has no perms whatsoever though ? In your version it would raise an exception because there is no `perms[0]`, in mine it would not filter the queryset at all. So I think you should add a test on `len(perms)` first. And unit test it.