Automatically trigger a 'change' event for the central form element in both analog and digital extension forms so that the right positions are auto-loaded in the dependen select
Code beautifying
Fix bug that was causing the impossibility to create a new digital extension because of an assertion (not null) in the model class

Also, added processing of takes in the controller, they were omitted and we had never realized it because there were no new digital extension since the app was launched
Fix comments
Allow $central_id to be null in 'findPositionsForCentralQb' method so we can return ALL available positions in a single query