Add command for "list-outdated"

[isc-shuliu]

Implement an outdated command mentioned in #427

[isc-kiyer]

@isc-shuliu this PR is related to #550 where part of running "update" should upgrade a module and run its upgrade steps (if any).

[isc-shuliu]

@isc-shuliu this PR is related to #550 where part of running "update" should upgrade a module and run its upgrade steps (if any).

Thanks for the heads-up! I'm aware of that hence posting it as a draft.