New command `cordova outdated`

... which is just `npm outdated` filtered down to only include platforms and plugins that are relevant to Cordova, not other Framework packages or similar.

This enables us to tell people to just run `cordova outdated` to learn what they have to update to get to a current state of all their libraries.

The issue names no files, tests, or entry points. Start by tracing how existing Cordova CLI commands are registered and how npm outdated is invoked; done means adding cordova outdated output that includes only relevant platforms and plugins while excluding unrelated packages.

Written by the indexing model from the issue text.