Support deleting trips from the client

TL;DR:
- Ensure Types.TripPK in Types.hs uses Calendar.Day for startDate
- Prefer verbiage "GotCreateTrip" to "CreatedTrip"
- Extend Utils.deleteWithCredentials to accept a body parameter
- Support a delete button in the UI

client/src/Utils.elm

@@ -62,17 +62,18 @@ postWithCredentials { url, body, expect } =
 
 deleteWithCredentials :
     { url : String
+    , body : Http.Body
     , expect : Http.Expect msg
     }
     -> Cmd msg
-deleteWithCredentials { url, expect } =
+deleteWithCredentials { url, body, expect } =
     Http.riskyRequest
         { url = url
         , headers = [ Http.header "Origin" Shared.clientOrigin ]
         , method = "DELETE"
         , timeout = Nothing
         , tracker = Nothing
-        , body = Http.emptyBody
+        , body = body
         , expect = expect
         }