Use FOS Elastica Paginator

Fix the way to retrieve and count results with FOS Elastica Paginator. (https://github.com/20minutes/SonataElasticaBundle/compare/fix-count?expand=1#diff-69eba46949213725c7f5b4ee3cd6a467L112)

With some inspirations of https://github.com/sonata-project/SonataDatagridBundle

Additionnaly, clean some part of codes, do not use deprecated elastica QueryText.
But a bit too far with BC Break, I admit, so maybe to refactor...