Allow access to Config API per-group

Summary:
- Adding tests for config access to specific groups
- Make Ushahidi_Authenticator work for resource assertions
- Use authenticator in Config API
- Add a2 rules for anonymous config access to features/map/site

Test Plan:
```
bin/behat -f progress -c application/tests/behat.yml application/tests/features/api.acl.feature
```

Reviewers: dkobia, eyedol, shadowhand

Reviewed By: shadowhand

Subscribers: srutto

Maniphest Tasks: T494

Differential Revision: https://phabricator.ushahidi.com/D244