Split/view test setup

@doctoryes mostly style changes, sorry. The important changes: factories.py, common.py not hardcoding slash separarated ck type, fixing course id collision in test_navigation.py (only applies to old mongo).

This fixes the unit test & acceptance test failures for using `create_course` instead of `create_item` still using only old mongo.

LMS-11441

I may add to this as I fix acceptance tests for split or create a separate PR. I wanted to show momentum on our JIRA board.
It had the added benefit of being able to quickly find all hardcoded uses of the default name which would break if we used split mongo. I'm somewhat in favor of unique naming, but not adamant.