OGM-424 Adding test for auto and manual flushing for JP-QL queries
OGM-424 Auto-flushing for native queries executed via classic API

* Also adding test for executing native query via JPA
OGM-424 Adding note on flush modes to MongoDB chapter in reference guide
OGM-369 Re-enabling test
OGM-574 Extracting dependency management information into separate BOM POM
OGM-574 Updating "Getting started" guide
OGM-574 Removing some unnecessary dependencies
OGM-574 Consistently using JTA 1.2
OGM-574 Updating some dependencies
OGM-574 Moving JTA dependency to BOM as it's referenced in the "Getting started" example
OGM-575 Don't expose mutator method on AssociationContext
Raising descriptive exception upon natural id look-ups which are not supported yet
OGM-590 Making sure nested embeddables can be accessed in MongoDB
OGM-548 Add ArrayHelper#EMPTY_STRING_ARRAY
OGM-548 Add ArrayHelper#indexOf
OGM-548 Update AssociationKey javadoc
OGM-548 Remove methods from AssociationKey that delegate to metadata
OGM-548 Add method AssociationPersister#createTargetKey
OGM-548 Add fields in RowKey and AssociationKeyMetadata

  * AssociationKeyMetadata#rowKeyIndexColumnNames
  * AssociationKeyMetadata#rowKeyTargetAssociationKeyColumnNames
  * AssociationKeyMetadata#rowKeyEntityKeyMetadata
  * RowKey#entityKey

  These methods allow a store to obtain information related to both side
  of the association.
OGM-548 Fix compilation errors for infinispan, couchdb, ehcache, mongodb

  The previous commit added some arguments to the constructor of RowKey
  and AssociationKeyMetadata but update only the core module