accounting: Make checkers show what they are doing

Before this change, all types of checkers showed "checking" after the
file name despite the fact that not all of them were checking.

After this change, they can show

- checking
- deleting
- hashing
- importing
- listing
- merging
- moving
- renaming

See: https://forum.rclone.org/t/what-is-rclone-checking-during-a-purge/35931/

backend/hasher/commands.go

@@ -161,7 +161,7 @@ func (f *Fs) dbImport(ctx context.Context, hashName, sumRemote string, sticky bo
 			if err := o.putHashes(ctx, hashMap{hashType: hash}); err != nil {
 				fs.Errorf(nil, "%s: failed to import: %v", remote, err)
 			}
-			accounting.Stats(ctx).NewCheckingTransfer(obj).Done(ctx, err)
+			accounting.Stats(ctx).NewCheckingTransfer(obj, "importing").Done(ctx, err)
 			doneCount++
 		}
 	})