News posting only allowd for admins

added a check in the Deelnemers-model if a user is an admin. In
NiewusController added the checks and makes a redirect to the index of
nieuws.
Changed htacces

htacces changed. Removed unused redirect for coreassets. Added a
indexIgnore for all files.
Adding nieuws support

Changed add-nieuws view and controller.Its possible to post nieuws and
format a urlpart of a nieuws-title.
Modified cfg.application.php

Added /politiekpoultje/ as site-root.