Clean up imports for contact_person.models, re #156
Clean up imports for contact_person.models, re #156

The `contact_person.models` module had many imports that were unused,
including imports of PublishingModel etc that will soon be rolled up
into more general ICEKit model mixins.

Cleaned up the module to reduce confusion.

ic-labs/django-icekit,ic-labs/django-icekit,ic-labs/django-icekit,ic-labs/django-icekit