Add possibility to sort by update field

Yes, we intend to add sorting to this. There's probably some confusion on how these are sorted and the labeling - it should be the last time anything related to the post (comments or answers) are added/updated that makes the posting pop to the top. The date displayed there may be associated with the original posting, not the related children. I'll verify.

We did have another request to display the number of comments and answers in two additional columns. Would this be helpful or valuable to have here?