Better error messages when we get a 500 error

[ryaanahmed]

There are a bunch of places that have default error messages like...

"Photo with id X is not in database."

... which are shown whenever the backend sends anything back except a 200 success code. This includes when we straight up crash the backend (in development), so can be misleading for a developer.

We should differentiate the error message in the frontend depending on the error code returned from the backend.