first pass at using new keys

It compiles. It sorta works. Several subcommands are FIXME marked and
broken, because things that used to accept separate --backend and --key
params need to be changed to accept just a --key that encodes all the key
info, now that there is metadata in keys.

Command/Unused.hs

@@ -126,4 +126,4 @@ tmpKeys = do
 			contents <- liftIO $ getDirectoryContents tmp
 			files <- liftIO $ filterM doesFileExist $
 				map (tmp </>) contents
-			return $ map (fileKey . takeFileName) files
+			return $ catMaybes $ map (fileKey . takeFileName) files