use bullet to detect n+1 issues

fix n+1 on org.departments

Fix social media n+1 at model level

remove n+1 tests in favour of using bullet

Remove count_queries tests
include translations in the admin document filter
include translations on roles
include organisation_type on admin orgs index
Merge pull request #400 from alphagov/remove-n-plus-one-tests

Use bullet to detect n+1 issues instead of tests