Port feature 9889

[*] Port from feature-9889: The mempool command has been added with subcommands list, proc, proc_all, dump, check, add_ca; the corresponding commands of the mempool_list type have been removed; they have been replaced by aliases for the mempool command. The output of transactions in mempool list has been reworked so that transactions are displayed in a more readable form, similar to the output of th_history with the -addr parameter. I made the mempool dump command to routinely output a datum dump from the mempool.