Reintroduce Debugging database handler; update main to allow for environment definition that will branch between all debug handlers or real effect handlers

src/Core.hs

@@ -25,7 +25,7 @@ type AppEff =
        , Error ServerError
        ]
 
-data AppEnv = AppEnv { pool :: Pool Connection }
+data AppEnv = AppEnv { pool :: Maybe (Pool Connection) }
 
 newtype UserId = UserId Int
   deriving (Show, Generic, FromField, ToField, FromHttpApiData, ToHttpApiData)