OGM-529 Delete CorrectNumberOfElementsTest

  It is going to be replaced by new tests split in different classes
OGM-529 Add new test classes to check the mapping in Neo4j
OGM-549 Check that no temporary nodes are left in the DB
OGM-549 Test the deletion of collection of elements
OGM-529 Create sequences at startup

  * Update the tests
  * Apply SEQUENCE label
  * Cache properly
  * Create unique constraint to avoid duplicated node for the same
    sequence
  * Sequences have a 'sequence_name' and 'current_value' properties
OGM-529 Clean up, remove unecessary constants
OGM-529 Add javadoc to NodeLabel