Wagtail-mailchimp-integration

What's Changed
* Refactoring and showing errors better by erick-otenyo in https://github.com/erick-otenyo/wagtail-mailchimp-integration/pull/3


**Full Changelog**: https://github.com/erick-otenyo/wagtail-mailchimp-integration/compare/0.0.9...0.1.0

- Refactor for inheritance resolution

- Catch error where `wagtailcore_site` relation is not migrated to db yet

- Update settings icon and refactor integration model inheritance

- Refactor page type checking