OGM-392 - Support for CouchDB's optimistic locking

(Based on top of https://github.com/hibernate/hibernate-ogm/pull/283, the actual diff of this PR can be found [here](https://github.com/gunnarmorling/hibernate-ogm/compare/gunnarmorling:OGM-443...gunnarmorling:OGM-392-new?expand=1). This new PR addresses the review remarks from https://github.com/hibernate/hibernate-ogm/pull/263.)

* Adding support for `@Generated` properties by refreshing entities with such fields after updates
* Using this to map the `_rev` attribute from CouchDB
* Enhancing `OgmCollectionPersister` and friends to refresh entities which contain "embedded" association information" after assocation updates; adding new method `GridDialect#isStoredInEntityStructure()` for that purpose