[JRO] Remove griddler.

Need to extract this functionality to its own gem

* Remove the reply-to text from emails
[JRO] Set old private topics to read
[JRO] Add caching around num of unread private topics

* Remove the check for whether a user can view their list of private
  topics in favor of just letting them go through to there and see a
  message saying nothing is there and would they like to create one
* Remove categories and sticky/locked from private topics since they're
  not used.
* Add a notifier for how many private topics there are.