allow using Aeson for streaming JSON output

Keeping Text.JSON use for now, because it seems a better fit for most of
the commands, which don't use very structured JSON objects, but just output
whatever fields suites them. But this lets Aeson be used when a more
structured data type is available to serialize to JSON.

Command/MetaData.hs

@@ -96,7 +96,7 @@ perform now o k = case getSet o of
 cleanup :: Key -> CommandCleanup
 cleanup k = do
 	l <- map unwrapmeta . fromMetaData <$> getCurrentMetaData k
-	maybeShowJSON l
+	maybeShowJSON (JSONObject l)
 	showLongNote $ unlines $ concatMap showmeta l
 	return True
   where