add VerifiedCopy data type

There should be no behavior changes in this commit, it just adds a more
expressive data type and adjusts code that had been passing around a [UUID]
or sometimes a Maybe Remote to instead use [VerifiedCopy].

Although, since some functions were taking two different [UUID] lists,
there's some potential for me to have gotten it horribly wrong.

Command/LockContent.hs

@@ -27,7 +27,7 @@ seek = withWords start
 -- dropping the lock.
 start :: [String] -> CommandStart
 start [ks] = do
-	ok <- lockContentShared k locksuccess
+	ok <- lockContentShared k (const locksuccess)
 		`catchNonAsync` (const $ return False)
 	liftIO $ if ok
 		then exitSuccess