[#456] Implement hook in /processor endpoint

* When a `image` action is submitted by a device, we try to match any
 `DeviceFileJobQueue` entity for that fileName, filtering by device or
  null
* `null` on `deviceId` means that we don't know the source of the image
* Next time a device ask for its notification, `missingFiles` and
  `missingUnknown`, shouldn't contain this image in the list