Improve Ebean enhancement when listing individual classes in config

Ebean enhancement currently does not cater for the use case where individual classes are listed in the `ebean.` config keys in `application.conf`, especially if those listed classes do not fall beneath the default `models.*` package.

This is due to Ebean's `OfflineFileTransform.process()` method, which expects **only** package names, and not individually listed classes.

This problem often manifests itself in the dreaded error:
```
PersistenceException: Error with [...] It has not been enhanced but it's
superClass [class play.db.ebean.Model] is? (You are not allowed to mix
enhancement in a single inheritance hierarchy) ...
```

This patch ensures that all listed classes and packages are checked for Ebean enhancement.

See  [Lighthouse ticket #343](https://play.lighthouseapp.com/projects/82401-play-20/tickets/343) for more information, as well as several threads on the mailing list.