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.

Assistant/Threads/Committer.hs

@@ -479,7 +479,7 @@ checkChangeContent change@(Change { changeInfo = i }) =
 			void $ if present
 				then queueTransfers "new file created" Next k (Just f) Upload
 				else queueTransfers "new or renamed file wanted" Next k (Just f) Download
-			handleDrops "file renamed" present k (Just f) Nothing
+			handleDrops "file renamed" present k (Just f) []
   where
 	f = changeFile change
 checkChangeContent _ = noop

Assistant/Threads/SanityChecker.hs

@@ -191,7 +191,7 @@ dailyCheck urlrenderer = do
 	void $ liftAnnex $ setUnusedKeys unused
 	forM_ unused $ \k -> do
 		unlessM (queueTransfers "unused" Later k Nothing Upload) $
-			handleDrops "unused" True k Nothing Nothing
+			handleDrops "unused" True k Nothing []
 
 	return True
   where

Assistant/Threads/TransferScanner.hs

@@ -157,7 +157,7 @@ expensiveScan urlrenderer rs = batch <~> do
 		present <- liftAnnex $ inAnnex key
 		liftAnnex $ handleDropsFrom locs syncrs
 			"expensive scan found too many copies of object"
-			present key (Just f) Nothing callCommandAction
+			present key (Just f) [] callCommandAction
 		liftAnnex $ do
 			let slocs = S.fromList locs
 			let use a = return $ mapMaybe (a key slocs) syncrs