Implementing delete function for photo

- Implement delete function for photo; deleting photo remove database record and file on aws S3.
- Implement function to assign front_page_photo to kitchen
Lastly, did you check to make sure this code handles the case where a particular `Photo` is the front-page photo of a `Kitchen`?  Is the `front_page_photo_id` field updated accordingly on the `kitchens` table or does it now contain a dangling reference?

This is why model tests are valuable.  You'd say something like this in RSpec

```ruby
expect {
  front_page_photo.destroy
}.to change { kitchen.front_page_photo }.to(nil)
```

Don't quote me on that verbatim.  You might need to reload the `kitchen` object from the database, for example.