Implemented multiple labels ability.

[chvarkov]

Added ability usage multiple labels.
See issue #54
Example of usage:

/**
 * @OGM\Node(labels={"Person"})
 */
class Person
{
}

/**
 * @OGM\Node(labels={"Student", "Person"})
 */
class Student extends Person
{
}

/**
 * @OGM\Node(labels={"Worker", "Person"})
 */
class Worker extends Person
{
}

 // Returns an array of Person from nodes (:Person)
$this->em->getRepository(Person::class)->findAll(); 

// Returns an array of Student from nodes (:Student:Person)
$this->em->getRepository(Student::class)->findAll(); 

// Returns an array of Student from nodes (:Worker:Person)
$this->em->getRepository(Worker::class)->findAll();  // Returns an array of Worker

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[ikwattro]

Thanks @chvarkov

This looks great ! One small question, in the case of a class with 2 labels, let's say Student and Person, and an index in the database on Person only, are the queries optimized to make use of the index ?

[chvarkov]

@ikwattro
Oops. I need better research it.
Maybe you see solution?