Complete new architecture for Config endpoint, fixes T849

Summary:
- convert controller from API to REST
- implement read, search, and update
- supporting changes as necessary

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

Reviewers: sheesh, vladimir, aMoniker

Reviewed By: aMoniker

Subscribers: ymohii, rjmackay, srutto

Maniphest Tasks: T849

Differential Revision: https://phabricator.ushahidi.com/D473