rename key2file and file2key

What these generate is not really suitable to be used as a filename,
which is why keyFile and fileKey further escape it. These are just
serializing Keys.

Also removed a quickcheck test that was very unlikely to test anything
useful, since it relied on random chance creating something that looks
like a serialized key. The other test is sufficient for testing what
that was intended to test anyway.

Command/LookupKey.hs

@@ -23,7 +23,7 @@ run _ file = seekSingleGitFile file >>= \case
 	Nothing -> return False
 	Just file' -> catKeyFile file' >>= \case
 		Just k  -> do
-			liftIO $ putStrLn $ key2file k
+			liftIO $ putStrLn $ serializeKey k
 			return True
 		Nothing -> return False