Orphan lists controller spec

**WIP** - was too excited to see if this would help us reach 80% coverage. It does!

JIRA https://osraav.atlassian.net/browse/OSRA-174

- Create controller spec for ActiveAdmin::OrphanListsController
- Couldn't find a better way to test the happy path for `new`, the current test is a bit lame - any input appreciated