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
Remember: writing tests are valuable not just because they protect against errors, but because they force you to think about what you code is _actually_ doing.  Over the course of writing a test you'll often realize that you forgot to account for something in your code that didn't occur to you when you originally wrote the code.