Show user confirmation after submitting food

Real basic, just let them know all is well.
Show the user last time's food on their checkin

If the user has eaten here before, we'll tell them what they had and how they
liked it.
Consider all foods at the current venue

The `Checkin` you just made probably doesn't have any `Food` on it yet. What we
really need is the `Food` from all previous `Checkin`s at that venue.

I tried to make it a `scope`, but Rails is being fussy.
Only reply on venues that have food

No sense asking you what you eat at the Gym, just places you're buying noms.