[ticket/11463] Add title attribute to topics in search results

We use this title attribute in viewforum_body.html, but not in
search_results.html. Perhaps we should, as this will maintain
consitency between all these topic view pages.

If this change is deemed worthwhile, here is the PR and ticket for it.
http://tracker.phpbb.com/browse/PHPBB3-11463

PHPBB3-11463