s/resource/entity/ when referring to REST

Syncs verbiage with the rest of the Apigility repositories.

- ::resource becomes ::entity
- configuration differentiates between collection and entity now, not collection
  and resource
Merge branch 'hotfix/resource-vs-entity'

Sync REST verbiage with other Apigility repos: resource -> entity (but not with
regards to ACL/RBAC resources!)