KS-4753 [Forum] Add appropriate exceptions when saving topic and post


- The call of listeners surrounded by try catch in all the methods that call them. By consequent, an appropriate message is added to notify the administrator.
- Another catch added to the call of save in UITopicForm, UIPostForm, UIQuickReplyForm to catch the NullPointerException.
- log.error added when saving topic to inform the administrator about the cause of the exception.