[RFR] #121 LayoutController - return workflow_states

LayoutController::getCollectionAction now returns an array of workflow_states for each Layout
An else is missing to this if statement. We have two differents cases:

- if a site_uid is provided, we return every layouts associated to the provided site_uid
- else (if no site_uid is provided), we return layout that are not associated to any site. They are used as model to the Layout tab in frontend. So we need it.

You surely need something like ``$qb->andWhere('l.site is null')`` in your else instruction block.