Cached counts app and management command
Order by -count, name as there are duplicate names
Use `get_or_create` to update counts

Thanks to @dracos for pointing out the `defaults` argument
Emit a person_added signal on creating new people
Refactor test to allow calling from elsewhere

It's useful to test creating a person from other places, so mock_create_person
does all the hard work, leaving the test case to just test for person creation
Use mock_create_person to test increments work
Add new counts to cache table
Remove unneeded imports
Add ReportsHomeView and nav item
Convert section to ul
Merge branch 'feature/candidates-counts'