OGM-548 Remove redundant properties from relationship in Neo4j

  * Remove foreign key properties from embedded nodes
  * Store only index columns in relationships
  * Remove TEMP nodes
  * Add relationhip for unidirectional *ToOne associations (in
    preparation of OGM-521)
OGM-548 Update Neo4j mapping unit tests

  * Relationships should not have properties except for indexes
  * Test fail for unexpected properties
  * Remove redundant columns for embedded associations
OGM-548 Add test to check the mapping of @ElementCollection with index in Neo4j
OGM-548 Add test to check the mapping of Maps in Neo4j
OGM-548 Add GraphLogger class to log information about graph elements
OGM-548 Log details of created/updated graph elements