Add a drush content-type-list command.

[serundeputy]

drush ctl

• list the content types on the site

drush ctl page

• list the details of the page content type

drush ctl page --fields

• list the fields on the page content type

drush ctl page --field=body

• list the details of the body field on the page content type

[serundeputy]

Added in https://github.com/backdrop-contrib/drush/pull/206