refs https://github.com/TryGhost/Team/issues/1546
- allows newsletters API to work with Admin API keys
- updates fixtures to add permissions to admin integration role for new sites
- adds migration to update existing sites to have correct permissions for role
- whitelists add/edit/read/browse on newsletters API for integrations
refs https://github.com/TryGhost/Team/issues/1533
- Needed to create the read newsletter endpoint to make the newsletter resource more consistent with the other resources
- Read is available to admins like other newsletter actions
refs https://github.com/TryGhost/Team/issues/1463
- Allow admins to perform all newsletter operations
- We can adjust and be more permissive in the future if needed
- Added the tests back as permissions are configured correctly now
- some tests are necessarily driven from the db
- these are like unit tests, except they only make sense if using the db - else you have to stub too much to make them worthwhile
- for these rare but important cases, we have the clear concept of integration tests
