Fix Doctrine ODM Support

[cbourgois]

Changes Faker\ORM\Doctrine\EntityPopulator to manage Doctrine ODM Documents.

Using the Class Doctrine\Common\Persistence\Mapping\ClassMetadata instead of Doctrine\ORM\Mapping\ClassMetadata

Managing ODM ReferenceOne as ORM One-To-One relations
(\Doctrine\ODM\MongoDB\Mapping\ClassMetadata does not have the getAssociationMappings function, I retrieve associationMappings using the exposed public var)

Changes generateId's signature to avoid using Doctrine\ORM\EntityManagerInterface; uses Doctrine\Common\Persistence\ObjectManager instead.

[GrahamCampbell]

This should be imported shouldn't it?

[cbourgois]

As described here : http://php.net/manual/en/language.operators.type.php (part.7) , no it shouldn't.

If I do something like this:

<?php
$faker = \Faker\Factory::create();
$isFooBar = $faker instanceof \Foo\Bar;

$isFooBarvalue is false.

The test can be rewritten like this if we want

 if ($this->class instanceof '\Doctrine\ORM\Mapping\ClassMetadata') {

If we want, for more clarity, we can split class to Faker\ORM\Doctrine\EntityPopulator and Faker\ORM\Doctrine\DocumentPopulator, and add an addDocument in Faker\ORM\Doctrine\Populator, for using Entity for ORM use and Document for ODM use.

[fzaninotto]

@beberlei Could you validate this PR for me please? I have no idea if it may break things or not...

[fzaninotto]

@lexicalbits any feedback on this one?

[lexicalbits]

@fzaninotto I don't think it bears on the issue I raised in #475, so no comments from me.

[fzaninotto]

Could you rebase on master?

[cbourgois]

It's done

[fzaninotto]

Thanks!