Add Photos to animals.

[smarbos]

Animal schema have a photos property, that will contain the path to the uploaded images.
https://github.com/feathersjs/docs/blob/master/guides/advanced/file-uploading.md

The path for this could be something like POST animals/:id/photos
The image should be in the payload, and we need the handler on this route, to save the image in the server and push the path to the corresponding animal photo's array.