Add entity-centric insert/update/delete methods to DatabaseClient

[mp911de]

DatabaseClient currently exposes methods such as insert().into(Person.class).using(new Person()) returing Map<String, Object> instead of entities. It would make sense to have an API that returns entities for an entity-centric approach. DatabaseClient could be used fully for entity-centric and SQL-centric use-cases. Entity-centric use-cases require the use of repositories.

The entity-centric approach could facilitate the usage of lifecycle callbacks and returning the modified entity.