Wagtail Report

"Hey, is there anywhere in the admin UI I can see a list of page types with counts?"

The idea so far is to provide a report of page types with page counts. So far it's assumed that all your page models extend wagtail.core.page, that's probably not good enough but it's a start.

Todos

• Is it useful for developers to see class inheritance in a dropdown row? Probably not, goes slightly against the publishing focus of the admin interface.
• Models that aren't page models but are models.Model
• Test
• Backwards compatability
• Readme and screenshot update
• Package up for pypi