Rewrote Admin_Skupiny to $this->render() format

Also:
* globally replaced View::getRedirectMessage() with $this->redirect()->...
* globally removed inline TODOs
* globally replaced <form action=""> if there was Request::getURI()
* fixed OFF switch
* added common RemovePrompt.inc for all administration
* fixed ORDER BY in DBSkupiny

Signed-off-by: dradancer <kuba.zarybnicky@post.cz>