Fix build with wai 0.3.0.

This version of wai changed the type of Middleware, so I cannot seem
to liftIO inside it. So, got rid of a lot of not really needed
complexity to use System.Log.Logger's logging stuff, and just use
the standard wai stdout logger when debug logging is enabled.

Format may change some, and it logs http to stdout instead of stderr
now. Doesn't matter for the webapp since both go to the same log anyway.

git-annex.cabal

@@ -189,7 +189,7 @@ Executable git-annex
   if flag(Webapp)
     Build-Depends:
      yesod, yesod-default, yesod-static, yesod-form, yesod-core,
-     http-types, transformers, wai, wai-logger, warp, warp-tls,
+     http-types, transformers, wai, wai-extra, warp, warp-tls,
      blaze-builder, crypto-api, hamlet, clientsession,
      template-haskell, data-default, aeson, network-conduit,
      shakespeare