Add Command method to BatchBuilder interface and implementation

batch.go

@@ -42,6 +42,10 @@ func NewBatchBuilder(dir string) (contract.BatchBuilder, error) {
 	}, nil
 }
 
+func (b *batchBuilder) Command() contract.CommandRun {
+	return b.command
+}
+
 func (b *batchBuilder) Clear() error {
 	args := nftCommand.Clear()
 	return b.command.Run(args...)