OGM-432 Adding test to make sure embedded collections are stored in the correct way in document stores

* Also enhancing test helpers to count embedded associations and collections separately
OGM-432 Considering association kind when storing associations

* Reverting "OGM-207 Removing AssociationKind enum as it is not required"
* Taking assocation kind into account when determining how to store associations
OGM-432 Some clean-up

* Passing all AssociationKey properties via constructor
* Improving docs
OGM-432 Always storing @EmbeddedCollection members embedded in the entity in CouchDB