This commit replaces the usage of Paris with Doctrine inside
MailPoet\API\JSON\v1\Forms::listing(). It also introduces a new class
MailPoet\Form\Listing\FormListingRepository that is used by listing() to
prepare the query that is executed by Doctrine and a new
MailPoet\API\JSON\ResponseBuilders\FormsResponseBuilder::buildForListing()
method to prepare the response that is returned by listing(). A few tests were
adjusted and new tests were added for the new class.
[MAILPOET-3036]
