use ThreadPresenter to render search results

@gwprice 

search result views were not originally refactored to use the presenter, but they did depend on CommentThread.to_hash which no longer supplies the fields ("unread_comment_count", "endorsed", "read").

this change passes search result views through the presenter as well, and does an extra inline step to add fields that are historically specific to search results.  i don't consider this a complete refactor of search, but it should actually make it a little faster, since it is using the new aggregation machinery.