logs: removed all log.Errors unhelpful to users

Let's save log.Error for things the user can take action on.
Moved all our diagnostics to log.Debug. We can ideally reduce them
even further.

blockservice.go

@@ -122,7 +122,7 @@ func (s *BlockService) GetBlocks(ctx context.Context, ks []u.Key) <-chan *blocks
 
 		rblocks, err := s.Exchange.GetBlocks(ctx, misses)
 		if err != nil {
-			log.Errorf("Error with GetBlocks: %s", err)
+			log.Debugf("Error with GetBlocks: %s", err)
 			return
 		}