Move @PreAuthorize tag from private to interface methods.

Security annotations does not works on private methods, just on public interfaces method which can be proxied.

TransactionalLastReadPostService.java

• private int calculatePostIndex(JCUser user, Topic topic, int pageNum, boolean pagingEnabled) {
• private void saveLastReadPost(JCUser user, Topic topic, int postIndex) {

TransactionalPollService.java

• private Poll vote(Poll poll, List<Long> selectedOptionIds, long branchId) {

TransactionalPostService.java

• private void updatePost(Post post, String postContent) (done in scope of JC-922)

TransactionalTopicService.java

• private Branch deleteTopic(Topic topic, long branchId) throws NotFoundException (done in scope of JC-922)
• private void moveTopic(Topic topic, Long branchId) throws NotFoundException (done in scope of JC-922)