Remove python-based auto-inheritance code?

[cogat]

The code that creates new Events and injects default values from the parent is pretty fragile. It also doesn't do any form validation and can potentially create invalid data (e.g. empty or duplicate slugs)

The IxC branch (409de8f) has implemented an admin method that works for django admin by populating a GET string for the new Event form. This even works with m2m fields. AFAICS this covers the main use case.

I'm fairly sure we can just strip out the inheritance code (and the callable default voodoo), but the tests need updating to reflect this.