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/Mirror.hs

@@ -65,7 +65,7 @@ startKey o afile key = case fromToOptions o of
 			Right False -> ifM (inAnnex key)
 				( do
 					numcopies <- getnumcopies
-					Command.Drop.startLocal afile numcopies key Nothing
+					Command.Drop.startLocal afile numcopies key []
 				, stop
 				)
   where