Review and clean up the current CLI implementation

[antonkorotkov]

The current CLI implementation is outdated and it is possible that it may just not work.
Need to review it and test/fix/cleanup or remove and start from scratch if needed.

[antonkorotkov]

I think the new command (wp sm) should be renamed to something else less generic because sm could interfere with another third-party command. How about wp stateless at least?

[planv]

The current CLI implementation is working.
Command upgrade uses for update postmeta from old structure to new.

Renamed command sm to stateless.

[antonkorotkov]

Ok, let it exist then.